Bacteria Total Daily Maximum Loads for 25 Guam Beaches by Guam Environmental Protection Agency

Guam Environmental Protection Agency BACTERIA TMDLS FOR TWENTY-FIVE GUAM BEACHES Prepared by Tetra Tech, Inc., 350 Indiana Street, Suite 500 Golden, CO 80401

December 2013 4:30 p.m. May 23, 2012

PHYSICAL ADDRESS 17-3304 Mariner Ave. Tiyan, GU

MAILING ADDRESS P.O. Box 22439, GMF Barrigada, GU 96921

Tel: (671)475-1658/59/28

Fax: (671) 475-8007 Visit us online at EPA.Guam.gov

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Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Contents 1.

Overview ........................................................................................................................................ 1

Setting ............................................................................................................................................ 3

Applicable Water Quality Standards ........................................................................................... 6

Water Quality Data ........................................................................................................................ 7 4.1. Available Information ................................................................................................................... 7 4.2. Spatial Distribution ....................................................................................................................... 8 4.3. Annual Analysis.......................................................................................................................... 11 4.4. Seasonal Variation ...................................................................................................................... 12 4.4.1. Seasonal Patterns in Water Quality Monitoring Data ....................................................... 12 4.4.2. Stream Flow and Seasonal Variation ................................................................................ 13 4.5. Duration Curve Analyses ............................................................................................................ 18 4.5.1. Flow Duration Curves ....................................................................................................... 18 4.5.2. Water Quality Duration Curves ........................................................................................ 19

Source Assessment.................................................................................................................... 23

5.1. 5.2. 5.3. 5.4.

Waste Water Sources .................................................................................................................. 23 Stormwater Sources .................................................................................................................... 28 Recreation and Other Sources .................................................................................................... 30 Summary ..................................................................................................................................... 32

Technical Approach and Linkage Analysis .............................................................................. 34 6.1. Options Considered .................................................................................................................... 34 6.1.1. Load-Based Approach (mass per unit time) ..................................................................... 35 6.1.2. Concentration-Based Method ........................................................................................... 35 6.1.3. Reference Method with Exceedance Day Frequencies ..................................................... 35 6.1.4. Tidal Prism Method .......................................................................................................... 36 6.1.5. Concentration-Based Duration Curve Method ................................................................. 36 6.2. Concentration-Based Duration Curve Linkage Analysis ........................................................... 36 6.2.1. Pattern Analysis ................................................................................................................ 37 6.2.2. Relationship to Other Indicators ....................................................................................... 44

TMDL Development .................................................................................................................... 47 7.1. Establishment of the TMDL ....................................................................................................... 47 7.2. Loading Capacity and Allocations.............................................................................................. 47 7.3. Margin of Safety ......................................................................................................................... 48

Individual Beach Assessments and TMDLs ............................................................................. 50

8.1. Adelup Beach Park (N-21) ......................................................................................................... 51 8.2. Adelup Point Beach (West of Adelup Point) (N-22) .................................................................. 61 8.3. Asan Bay Beach (N-14) .............................................................................................................. 71 8.4. Piti Bay (N-15) ........................................................................................................................... 81 8.5. Santos Memorial Park Beach (N-16) .......................................................................................... 91 8.6. United Seamen’s Service (N-17) .............................................................................................. 100 8.7. Outhouse Beach (N-18) ............................................................................................................ 110 8.8. Family Beach (N-19) ................................................................................................................ 120 8.9. Port Authority Beach (N-20) .................................................................................................... 130 8.10. Togcha Beach – Namo River (S-02) ........................................................................................ 140 8.11. Togcha Beach – Agat Bay (S-03) ............................................................................................. 149 8.12. Togcha Beach – Beach at SCA (S-17) ..................................................................................... 158

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

8.13. Bangi Beach (S-04)................................................................................................................... 167 8.14. Nimitz Beach (S-05) ................................................................................................................. 177 8.15. Umatac Bay (S-06) ................................................................................................................... 187 8.16. Toguan Bay (S-07) ................................................................................................................... 196 8.17. Merizo Pier – Mamaon Channel (S-08).................................................................................... 206 8.18. Inarajan Pool (S-09) .................................................................................................................. 216 8.19. Inarajan Bay (S-10)................................................................................................................... 226 8.20. Talofofo Bay (S-11) .................................................................................................................. 235 8.21. First Beach - Talofofo (S-18) ................................................................................................... 245 8.22. Ipan Beach (S-12) ..................................................................................................................... 255 8.23. Togcha Bay - Talofofo (S-13) .................................................................................................. 264 8.24. Tagachang Beach (S-14)........................................................................................................... 274 8.25. Pago Bay (S-15) ........................................................................................................................ 284 9.

10.

Implementation ......................................................................................................................... 294 9.1. Implementation Prioritization ................................................................................................... 294 9.2. Source Characterization ............................................................................................................ 300 9.3. Implementation Activities ........................................................................................................ 303 9.3.1. Existing Programs ........................................................................................................... 304 9.3.2. Specific Implementation Opportunities (BMPs) ............................................................ 309 9.4. Monitoring and TMDL Re-Assessment ................................................................................... 315 References................................................................................................................................. 316

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figures Figure 2-1. Location of Guam TMDL project area beaches ......................................................................... 3 Figure 4-1. Spatial distribution of beach advisories ..................................................................................... 9 Figure 4-2. Spatial distribution of beach monitoring data ............................................................................ 9 Figure 4-3. 90th percentile bacteria concentrations at each beach monitoring site ..................................... 10 Figure 4-4. Average rolling geomean for each beach monitoring site ........................................................ 11 Figure 4-5. Annual analysis for Togcha Bay .............................................................................................. 12 Figure 4-6. Seasonal variation at Togcha Bay ............................................................................................ 13 Figure 4-7. Location of USGS gaging stations and annual rainfall distribution ........................................ 15 Figure 4-8. Seasonal variation of flows for the Pago River ........................................................................ 16 Figure 4-9. Seasonal variation of flows for the AplachoRiver ................................................................... 16 Figure 4-10. Seasonal variation of flows for the La Sa Fua River.............................................................. 17 Figure 4-11. Seasonal variation of flows for the Almagosa River.............................................................. 17 Figure 4-12. Flow duration curve for Almagosa River Gage (USGS Gage 16848100) ............................. 19 Figure 4-13. Water quality duration analysis for Togcha Bay .................................................................... 20 Figure 4-14. Detailed water quality duration analysis for Togcha Bay ...................................................... 21 Figure 4-15. Wet versus dry seasonal duration curve analysis for Togcha Bay ......................................... 22 Figure 5-1. Location of non-sewered buildings in the TMDL project area ................................................ 24 Figure 5-2. Location of pump stations and bacteria-discharging permitted facilities ................................ 27 Figure 5-3. Location of impervious surface in theTMDL project area ....................................................... 29 Figure 5-4. Location of marinas in the TMDL project area ........................................................................ 31 Figure 6-1. Wet versus dry season comparison for Togcha Bay ................................................................ 40 Figure 8-1. Location of Adelup Beach Park relative to other TMDL sites ................................................ 51 Figure 8-2. Beach advisory frequency at Adelup Beach Park .................................................................... 52 Figure 8-3. Enterococci data analysis at Adelup Beach Park ..................................................................... 53 Figure 8-4. Annual analysis of enterococcus data for Adelup Beach Park ................................................. 54 Figure 8-5. Seasonal variation at Adelup Beach Park ................................................................................ 55 Figure 8-6. Water quality duration analysis of Adelup Beach Park ........................................................... 56 Figure 8-7. Detailed water quality duration analysis of Adelup Beach Park .............................................. 56 Figure 8-8. Wet versus dry seasonal analysis for Adelup Beach Park ....................................................... 57 Figure 8-9. Land cover and location of Adelup Beach Park relative to potential source areas .................. 58 Figure 8-10. Location of Adelup Beach Park relative to zoned land use ................................................... 59 Figure 8-11. Location of Adelup Point Beach relative to other TMDL sites ............................................. 61 Figure 8-12. Beach advisory frequency at Adelup Point Beach ................................................................. 62 Figure 8-13. Enterococci data analysis at Adelup Point Beach .................................................................. 63 Figure 8-14. Annual analysis of enterococcus data for Adelup Point Beach ............................................. 64 Figure 8-15. Seasonal variation at Adelup Point Beach ............................................................................. 65 Figure 8-16. Water quality duration analysis of Adelup Point Beach ........................................................ 66 Figure 8-17. Detailed water quality duration analysis of Adelup Point Beach ........................................... 66 Figure 8-18. Wet versus dry seasonal analysis for Adelup Point Beach .................................................... 67

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Figure 8-19. Land cover and location of Adelup Point Beach relative to potential source areas ............... 68 Figure 8-20. Location of Adelup Point Beach relative to zoned land use .................................................. 69 Figure 8-21. Location of Asan Bay Beach relative to other TMDL sites ................................................... 71 Figure 8-22. Beach advisory frequency at Asan Bay Beach ....................................................................... 72 Figure 8-23. Enterococci data analysis at Asan Bay Beach ........................................................................ 73 Figure 8-24. Annual analysis of enterococcus data for Asan Bay Beach ................................................... 74 Figure 8-25. Seasonal variation at Asan Bay Beach ................................................................................... 75 Figure 8-26. Water quality duration analysis of Asan Bay Beach .............................................................. 76 Figure 8-27. Detailed water quality duration analysis of Asan Bay Beach ................................................ 76 Figure 8-28. Wet versus dry seasonal analysis for Asan Bay Beach .......................................................... 77 Figure 8-29. Land cover and location of Asan Bay Beach relative to potential source areas .................... 78 Figure 8-30. Location of Asan Bay Beach relative to zoned land use ........................................................ 79 Figure 8-31. Location of Piti Bay relative to other TMDL sites................................................................. 81 Figure 8-32. Beach advisory frequency at Piti Bay .................................................................................... 82 Figure 8-33. Enterococci data analysis at Piti Bay ..................................................................................... 83 Figure 8-34. Annual analysis of enterococcus data for Piti Bay ................................................................. 84 Figure 8-35. Seasonal variation at Piti Bay................................................................................................. 85 Figure 8-36. Water quality duration analysis of Piti Bay ........................................................................... 86 Figure 8-37. Detailed water quality duration analysis of Piti Bay .............................................................. 86 Figure 8-38. Wet versus dry seasonal analysis for Piti Bay ........................................................................ 87 Figure 8-39. Land cover and location of Piti Bay relative to potential source areas .................................. 88 Figure 8-40. Location of Piti Bay relative to zoned land use ..................................................................... 89 Figure 8-41. Location of Santos Memorial Park Beach relative to other TMDL sites ............................... 91 Figure 8-42. Enterococci data analysis at Santos Memorial Park Beach .................................................... 92 Figure 8-43. Annual analysis of enterococcus data for Santos Memorial Park Beach ............................... 93 Figure 8-44. Seasonal variation at Santos Memorial Park Beach ............................................................... 94 Figure 8-45. Water quality duration analysis of Santos Memorial Park Beach .......................................... 95 Figure 8-46. Detailed water quality duration analysis of Santos Memorial Park Beach ............................ 95 Figure 8-47. Wet versus dry seasonal analysis for Santos Memorial Park Beach ...................................... 96 Figure 8-48. Land cover and location of Santos Memorial Park Beach relative to potential source areas .................................................................................................................................................... 97 Figure 8-49. Location of Santos Memorial Park Beach relative to zoned land use .................................... 98 Figure 8-50. Location of United Seamen’s Service relative to other TMDL sites ................................... 100 Figure 8-51. Beach advisory frequency at United Seamen’s Service ....................................................... 101 Figure 8-52. Enterococci data analysis at United Seamen’s Service ........................................................ 102 Figure 8-53. Annual analysis of enterococcus data for United Seamen’s Service ................................... 103 Figure 8-54. Seasonal variation at United Seamen’s Service ................................................................... 104 Figure 8-55. Water quality duration analysis of United Seamen’s Service .............................................. 105 Figure 8-56. Detailed water quality duration analysis of United Seamen’s Service ................................ 105 Figure 8-57. Wet versus dry seasonal analysis for United Seamen’s Service .......................................... 106

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-58. Land cover and location of United Seamen’s Service relative to potential source areas .................................................................................................................................................. 107 Figure 8-59. Location of United Seamen’s Service relative to zoned land use ........................................ 108 Figure 8-60. Location of Outhouse Beach relative to other TMDL sites ................................................. 110 Figure 8-61. Beach advisory frequency at Outhouse Beach ..................................................................... 111 Figure 8-62. Enterococci data analysis at Outhouse Beach ...................................................................... 112 Figure 8-63. Annual analysis of enterococcus data for Outhouse Beach ................................................. 113 Figure 8-64. Seasonal variation at Outhouse Beach ................................................................................. 114 Figure 8-65. Water quality duration analysis of Outhouse Beach ............................................................ 115 Figure 8-66. Detailed water quality duration analysis of Outhouse Beach .............................................. 115 Figure 8-67. Wet versus dry seasonal analysis for Outhouse Beach ........................................................ 116 Figure 8-68. Land cover and location of Outhouse Beach relative to potential source areas ................... 117 Figure 8-69. Location of Outhouse Beach relative to zoned land use ...................................................... 118 Figure 8-70. Location of Family Beach relative to other TMDL sites ..................................................... 120 Figure 8-71. Beach advisory frequency at Family Beach ......................................................................... 121 Figure 8-72. Enterococci data analysis at Family Beach .......................................................................... 122 Figure 8-73. Annual analysis of enterococcus data for Family Beach ..................................................... 123 Figure 8-74. Seasonal variation at Family Beach ..................................................................................... 124 Figure 8-75. Water quality duration analysis of Family Beach ................................................................ 125 Figure 8-76. Detailed water quality duration analysis of Family Beach .................................................. 125 Figure 8-77. Wet versus dry seasonal analysis for Family Beach ............................................................ 126 Figure 8-78. Land cover and location of Family Beach relative to potential source areas ....................... 127 Figure 8-79. Location of Family Beach relative to zoned land use .......................................................... 128 Figure 8-80. Location of Port Authority Beach relative to other TMDL sites ......................................... 130 Figure 8-81. Beach advisory frequency at Port Authority Beach ............................................................. 131 Figure 8-82. Enterococci data analysis at Port Authority Beach .............................................................. 132 Figure 8-83. Annual analysis of enterococcus data for Port Authority Beach ......................................... 133 Figure 8-84. Seasonal variation at Port Authority Beach ......................................................................... 134 Figure 8-85. Water quality duration analysis of Port Authority Beach .................................................... 135 Figure 8-86. Detailed water quality duration analysis of Port Authority Beach ....................................... 135 Figure 8-87. Wet versus dry seasonal analysis for Port Authority Beach ................................................ 136 Figure 8-88. Land cover and location of Port Authority Beach relative to potential source areas ........... 137 Figure 8-89. Location of Port Authority Beach relative to zoned land use .............................................. 138 Figure 8-90. Location of Togcha Beach near Namo River relative to other TMDL sites ........................ 140 Figure 8-91. Beach advisory frequency at Togcha Beach near Namo River ............................................ 141 Figure 8-92. Enterococci data analysis at Togcha Beach near Namo River ............................................. 141 Figure 8-93. Annual analysis of enterococcus data for Togcha Beach near Namo River ........................ 142 Figure 8-94. Seasonal variation at Togcha Beach near Namo River ........................................................ 143 Figure 8-95. Water quality duration analysis of Togcha Beach near Namo River ................................... 144 Figure 8-96. Detailed water quality duration analysis of Togcha Beach near Namo River ..................... 144 Figure 8-97. Wet versus dry seasonal analysis for Togcha Beach near Namo River ............................... 145

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-98. Land cover and location of Togcha Beach near Namo River relative to potential source areas ...................................................................................................................................... 146 Figure 8-99. Location of Togcha Beach near Namo River relative to zoned land use ............................. 147 Figure 8-100. Location of Agat Bay relative to other TMDL sites .......................................................... 149 Figure 8-101. Beach advisory frequency at Agat Bay .............................................................................. 150 Figure 8-102. Enterococci data analysis at Agat Bay ............................................................................... 150 Figure 8-103. Annual analysis of enterococcus data for Agat Bay .......................................................... 151 Figure 8-104. Seasonal variation at Agat Bay .......................................................................................... 152 Figure 8-105. Water quality duration analysis of Agat Bay ..................................................................... 153 Figure 8-106. Detailed water quality duration analysis of Agat Bay ........................................................ 153 Figure 8-107. Wet versus dry seasonal analysis for Agat Bay ................................................................. 154 Figure 8-108. Land cover and location of Agat Bay relative to potential source areas ............................ 155 Figure 8-109. Location of Agat Bay relative to zoned land use ............................................................... 156 Figure 8-112. Location of Togcha Beach at SCA relative to other TMDL sites ...................................... 158 Figure 8-113. Beach advisory frequency at Togcha Beach at SCA .......................................................... 159 Figure 8-114. Enterococci data analysis at Togcha Beach at SCA ........................................................... 159 Figure 8-115. Annual analysis of enterococcus data for Togcha Beach at SCA ...................................... 160 Figure 8-116. Seasonal variation at Togcha Beach at SCA ...................................................................... 161 Figure 8-117. Water quality duration analysis of Togcha Beach at SCA ................................................. 162 Figure 8-118. Detailed water quality duration analysis of Togcha Beach at SCA ................................... 162 Figure 8-119. Wet versus dry seasonal analysis for Togcha Beach at SCA ............................................. 163 Figure 8-120. Land cover and location of Togcha Beach at SCA relative to potential source areas ....... 164 Figure 8-121. Location of Togcha Beach at SCA relative to zoned land use ........................................... 165 Figure 8-122. Location of Bangi Beach relative to other TMDL sites ..................................................... 167 Figure 8-123. Beach advisory frequency at Bangi Beach ......................................................................... 168 Figure 8-124. Enterococci data analysis at Bangi Beach .......................................................................... 169 Figure 8-125. Annual analysis of enterococcus data for Bangi Beach ..................................................... 170 Figure 8-126. Seasonal variation at Bangi Beach ..................................................................................... 171 Figure 8-127. Water quality duration analysis of Bangi Beach ................................................................ 172 Figure 8-128. Detailed water quality duration analysis of Bangi Beach .................................................. 172 Figure 8-129. Wet versus dry seasonal analysis for Bangi Beach ............................................................ 173 Figure 8-130. Land cover and location of Bangi Beach relative to potential source areas....................... 174 Figure 8-131. Location of Bangi Beach relative to zoned land use .......................................................... 175 Figure 8-132. Location of Nimitz Beach relative to other TMDL sites ................................................... 177 Figure 8-133. Beach advisory frequency at Nimitz Beach ....................................................................... 178 Figure 8-134. Enterococci data analysis at Nimitz Beach ........................................................................ 179 Figure 8-135. Annual analysis of enterococcus data for Nimitz Beach .................................................... 180 Figure 8-136. Seasonal variation at Nimitz Beach ................................................................................... 181 Figure 8-137. Water quality duration analysis of Nimitz Beach .............................................................. 182 Figure 8-138. Detailed water quality duration analysis of Nimitz Beach ................................................. 182 Figure 8-139. Wet versus dry seasonal analysis for Nimitz Beach .......................................................... 183

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-140. Land cover and location of Nimitz Beach relative to potential source areas ..................... 184 Figure 8-141. Location of Nimitz Beach relative to zoned land use ........................................................ 185 Figure 8-144. Location of Umatac Bay relative to other TMDL sites ...................................................... 187 Figure 8-145. Beach advisory frequency at Umatac Bay ......................................................................... 188 Figure 8-146. Enterococci data analysis at Umatac Bay .......................................................................... 188 Figure 8-147. Annual analysis of enterococcus data for Umatac Bay ...................................................... 189 Figure 8-148. Seasonal variation at Umatac Bay ...................................................................................... 190 Figure 8-149. Water quality duration analysis of Umatac Bay ................................................................. 190 Figure 8-150. Detailed water quality duration analysis of Umatac Bay ................................................... 191 Figure 8-151. Wet versus dry seasonal analysis for Umatac Bay ............................................................. 192 Figure 8-152. Land cover and location of Umatac Bay relative to potential source areas ....................... 193 Figure 8-153. Location of Umatac Bay relative to zoned land use ........................................................... 194 Figure 8-154. Location of Toguan Bay relative to other TMDL sites ...................................................... 196 Figure 8-155. Beach advisory frequency at Toguan Bay .......................................................................... 197 Figure 8-156. Instantaneous and geomean water quality data at Toguan Bay ......................................... 198 Figure 8-157. Annual analysis for Toguan Bay ........................................................................................ 199 Figure 8-158. Seasonal variation at Toguan Bay ...................................................................................... 200 Figure 8-159. Water quality duration analysis of Toguan Bay ................................................................. 201 Figure 8-160. Detailed water quality duration analysis of Toguan Bay ................................................... 201 Figure 8-161. Wet versus dry seasonal comparison at Toguan Bay ......................................................... 202 Figure 8-162. Land cover and location of Toguan Bay relative to potential source areas ....................... 203 Figure 8-163. Location of Toguan Bay relative to zoned land use ........................................................... 204 Figure 8-164. Location of Merizo Pier - Mamaon Channel relative to other TMDL sites ....................... 206 Figure 8-165. Beach advisory frequency at Merizo Pier – Mamaon Channel .......................................... 207 Figure 8-166. Enterococci data analysis at Merizo Pier – Mamaon Channel ........................................... 208 Figure 8-167. Annual analysis for Merizo Pier - Mamaon Channel site .................................................. 209 Figure 8-168. Seasonal variation at Merizo Pier - Mamaon Channel ....................................................... 210 Figure 8-169. Water quality duration analysis of Merizo Pier - Mamaon Channel .................................. 211 Figure 8-170. Detailed water quality duration analysis of Merizo Pier - Mamaon Channel .................... 211 Figure 8-171. Wet versus dry season comparison for Merizo Pier - Mamaon Channel ........................... 212 Figure 8-172. Land cover and location of Merizo Pier – Mamaon Channel relative to potential source areas ...................................................................................................................................... 213 Figure 8-173. Location of Merizo Pier – Mamaon Channelrelative to zoned land use ............................ 214 Figure 8-174. Location of Inarajan Pool relative to other TMDL sites .................................................... 216 Figure 8-175. Beach advisory frequency at Inarajan Pool ........................................................................ 217 Figure 8-176. Enterococci data analysis at Inarajan Pool ......................................................................... 218 Figure 8-177. Annual analysis for Inarajan Pool site................................................................................ 219 Figure 8-178. Seasonal variation at Inarajan Pool .................................................................................... 220 Figure 8-179. Water quality duration analysis of Inarajan Pool ............................................................... 221 Figure 8-180. Detailed water quality duration analysis of Inarajan Pool ................................................. 221 Figure 8-181. Wet versus dry season comparison for Inarajan Pool ........................................................ 222

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Figure 8-182. Land cover and location of Inarajan Pool relative to potential source areas ...................... 223 Figure 8-183. Location of Inarajan Pool relative to zoned land use ......................................................... 224 Figure 8-184. Location of Inarajan Bay relative to other TMDL sites ..................................................... 226 Figure 8-185. Beach advisory frequency at Inarajan Bay ......................................................................... 227 Figure 8-186. Enterococci data analysis at Inarajan Bay .......................................................................... 227 Figure 8-187. Annual analysis for Inarajan Bay site ................................................................................ 228 Figure 8-188. Seasonal variation at Inarajan Bay ..................................................................................... 229 Figure 8-189. Water quality duration analysis of Inarajan Bay ................................................................ 230 Figure 8-190. Detailed water quality duration analysis of Inarajan Bay .................................................. 230 Figure 8-191. Wet versus dry season comparison for Inarajan Bay ......................................................... 231 Figure 8-192. Land cover and location of Inarajan Bay relative to potential source areas....................... 232 Figure 8-193. Location of Inarajan Bay relative to zoned land use .......................................................... 233 Figure 8-194. Location of Talofofo Bay relative to other TMDL sites .................................................... 235 Figure 8-195. Beach advisory frequency at Talofofo Bay ........................................................................ 236 Figure 8-196. Enterococci data analysis at Talofofo Bay ......................................................................... 237 Figure 8-197. Annual analysis for Talofofo Bay site................................................................................ 238 Figure 8-198. Seasonal variation at Talofofo Bay .................................................................................... 239 Figure 8-199. Water quality duration analysis of Talofofo Bay ............................................................... 240 Figure 8-200. Detailed water quality duration analysis of Talofofo Bay ................................................. 240 Figure 8-201. Wet versus dry season comparison for Talofofo Bay ........................................................ 241 Figure 8-202. Land cover and location of Talofofo Bay relative to potential source areas ...................... 242 Figure 8-203. Location of Talofofo Bay relative to zoned land use ......................................................... 243 Figure 8-204. Location of First Beach - Talofofo relative to other TMDL sites ...................................... 245 Figure 8-205. Beach advisory frequency at First Beach – Talofofo ......................................................... 246 Figure 8-206. Enterococci data analysis at First Beach – Talofofo .......................................................... 247 Figure 8-207. Annual analysis for First Beach - Talofofo site ................................................................. 248 Figure 8-208. Seasonal variation at First Beach - Talofofo ...................................................................... 249 Figure 8-209. Water quality duration analysis of First Beach (Ipan Point Beach) ................................... 250 Figure 8-210. Detailed water quality duration analysis of First Beach (Ipan Point Beach) ..................... 250 Figure 8-211. Wet versus dry seasonal analysis for First Beach (Ipan Point Beach) ............................... 251 Figure 8-212. Land cover and location of First Beach - Talofofo relative to potential source areas ....... 252 Figure 8-213. Location of First Beach - Talofofo relative to zoned land use ........................................... 253 Figure 8-214. Location of Ipan Beach relative to other TMDL sites ....................................................... 255 Figure 8-215. Beach advisory frequency at Ipan Beach ........................................................................... 256 Figure 8-216. Enterococci data analysis at Ipan Beach ............................................................................ 257 Figure 8-217. Annual analysis for Ipan Beach site ................................................................................... 258 Figure 8-218. Seasonal variation at Ipan Beach ....................................................................................... 258 Figure 8-219. Water quality duration analysis of Ipan Beach .................................................................. 259 Figure 8-220. Detailed water quality analysis of Ipan Beach ................................................................... 260 Figure 8-221. Wet versus dry season analysis for Ipan Beach ................................................................. 260 Figure 8-222. Land cover and location of Ipan Beach relative to potential source areas ......................... 261

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Figure 8-223. Location of Ipan Beach relative to zoned land use ............................................................ 262 Figure 8-224. Location of Togcha Bay - Talofofo relative to other TMDL sites ..................................... 264 Figure 8-225. Beach advisory frequency at Togcha Bay - Talofofo ........................................................ 265 Figure 8-226. Enterococci data analysis at Togcha Bay - Talofofo .......................................................... 266 Figure 8-227. Annual enterococcus data analysis for Togcha Bay - Talofofo site ................................... 267 Figure 8-228. Seasonal variation at Togcha Bay - Talofofo ..................................................................... 268 Figure 8-229. Water quality duration analysis of Togcha Bay - Talofofo ................................................ 269 Figure 8-230. Detailed water quality duration analysis of Togcha Bay – Talofofo Beach ...................... 269 Figure 8-231. Wet versus dry seasonal analysis of Togcha Bay – Talofofo Beach ................................. 270 Figure 8-232. Land cover and location of Togcha Bay - Talofofo relative to potential source areas ...... 271 Figure 8-233. Location of Togcha Bay - Talofofo relative to zoned land use .......................................... 272 Figure 8-234. Location of Tagachang Beach relative to other TMDL sites ............................................. 274 Figure 8-235. Beach advisory frequency at Tagachang Beach ................................................................. 275 Figure 8-236. Enterococci data analysis at Tagachang Beach .................................................................. 276 Figure 8-237. Annual analysis of enterococcus data for Tagachang Beach ............................................. 277 Figure 8-238. Seasonal variation at Tagachang Beach ............................................................................. 278 Figure 8-239. Water quality duration analysis of Tagachang Beach ........................................................ 279 Figure 8-240. Detailed water quality duration analysis of Tagachang Beach .......................................... 279 Figure 8-241. Wet versus dry seasonal analysis for Tagachang Beach .................................................... 280 Figure 8-242. Land cover and location of Tagachang Beach relative to potential source areas............... 281 Figure 8-243. Location of Tagachang Beach relative to zoned land use .................................................. 282 Figure 8-244. Location of Pago Bay relative to other TMDL sites .......................................................... 284 Figure 8-245. Beach advisory frequency at Pago Bay .............................................................................. 285 Figure 8-246. Enterococci data analysis at Pago Bay ............................................................................... 286 Figure 8-247. Annual analysis of enterococcus data for Pago Bay .......................................................... 287 Figure 8-248. Seasonal variation at Pago Bay .......................................................................................... 288 Figure 8-249. Water quality duration analysis of Pago Bay ..................................................................... 289 Figure 8-250. Detailed water quality duration analysis of Pago Bay ....................................................... 289 Figure 8-251. Wet versus dry seasonal analysis for Pago Bay ................................................................. 290 Figure 8-252. Land cover and location of Pago Bay relative to potential source areas ............................ 291 Figure 8-253. Location of Pago Bay relative to zoned land use ............................................................... 292

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Tables Table 1-1. Waterbodies covered under the Bacteria TMDLs for Twenty-five Guam Beaches .................... 1 Table 2-1. Guam TMDL project area beaches .............................................................................................. 4 Table 4-1. Inventory of Bacteria TMDL monitoring data (2001-2011) ....................................................... 7 Table 4-2. Water quality stations and USGS flow gages ............................................................................ 14 Table 5-1. Reported SSOs that may affect TMDL Beaches (September to December 2011) .................... 25 Table 5-2. Point sources with NPDES permits that may affect the TMDL beaches .................................. 26 Table 5-3. Point sources without NPDES permits that may affect the TMDL beaches ............................. 26 Table 5-4. Pollution threats for the TMDL project area beaches ................................................................ 32 Table 5-5. Pollution threat code definitions ................................................................................................ 33 Table 6-1. TMDL beach data summary (Geometric Mean – year round) .................................................. 38 Table 6-2. TMDL beach data summary (90th percentile – year round) ...................................................... 39 Table 6-3. TMDL beach data summary (Geometric Mean – dry season) .................................................. 41 Table 6-4. TMDL beach data summary (Geometric Mean – wet season) .................................................. 42 Table 6-5. TMDL beach data summary (90th percentile – dry season) ...................................................... 43 Table 6-6. TMDL beach data summary (90th percentile – wet season) ...................................................... 44 Table 6-7. Summary of available turbidity data ........................................................................................ 45 Table 7-1. TMDLs and Allocations for M-2 Beaches ................................................................................ 48 Table 7-2. TMDLs and Allocations for M-3 Beaches ................................................................................ 48 Table 8-1. GIS data layers considered in individual beach assessments .................................................... 50 Table 8-2. Beach specific potential source summary (Site N-21: Adelup Beach Park) ............................. 58 Table 8-3. TMDL summary (Site N-21: Adelup Beach Park) .................................................................... 60 Table 8-4. Reductions required to meet the TMDL (Site N-21: Adelup Beach Park) ............................... 60 Table 8-5. Beach specific potential source summary (Site N-22: Adelup Point Beach) ............................ 68 Table 8-6. TMDL summary (Site N-22: Adelup Point Beach)................................................................... 70 Table 8-7. Reductions required to meet the TMDL (Site N-21: Adelup Point Beach) .............................. 70 Table 8-8. Beach specific potential source summary (Site N-14: Asan Bay Beach) .................................. 78 Table 8-9. TMDL summary (Site N-14: Asan Bay Beach) ........................................................................ 80 Table 8-10. Reductions required to meet the TMDL (Site N-14: Asan Bay Beach) .................................. 80 Table 8-11. Beach specific potential source summary (Site N-15: Piti Bay) ............................................. 88 Table 8-12. TMDL summary (Site N-15: Piti Bay) .................................................................................... 90 Table 8-13. Reductions required to meet the TMDL (Site N-15: Piti Bay)................................................ 90 Table 8-14. Beach specific potential source summary (Site N-16: Santos Memorial Park Beach)............ 97 Table 8-15. TMDL summary (Site N-16: Santos Memorial Park Beach) .................................................. 99 Table 8-16. Reductions required to meet the TMDL (Site N-16: Santos Memorial Park Beach) .............. 99 Table 8-17. Beach specific potential source summary (Site N-17: United Seamen’s Service) ................ 107 Table 8-18. TMDL summary (Site N-17: United Seamen’s Service) ...................................................... 109 Table 8-19. Reductions required to meet the TMDL (Site N-17: United Seaman’s Service) .................. 109 Table 8-20. Beach specific potential source summary (Site N-18: Outhouse Beach) .............................. 117 Table 8-21. TMDL summary (Site N-18: Outhouse Beach) .................................................................... 119

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Twenty Five Guam Beaches

Table 8-22. Reductions required to meet the TMDL and M-2 WQS (Site N-18: Outhouse Beach) ........ 119 Table 8-23. Beach specific potential source summary (Site N-19: Family Beach) .................................. 127 Table 8-24. TMDL summary (Site N-19: Family Beach) ........................................................................ 129 Table 8-25. Reductions required to meet the TMDL (Site N-19: Family Beach) .................................... 129 Table 8-26. Beach specific potential source summary (Site N-20: Port Authority Beach) ...................... 137 Table 8-27. TMDL summary (Site N-20: Port Authority Beach)............................................................. 139 Table 8-28. Reductions required to meet the TMDL and M-2 WQS (Site N-20: Port Authority Beach) ............................................................................................................................................... 139 Table 8-29. Beach specific potential source summary (Site S-02: Togcha Beach near Namo River) ..... 146 Table 8-30. TMDL summary (Site S-02: Togcha Beach near Namo River) ............................................ 148 Table 8-31. Reductions required to meet the TMDL (Site S-02: Togcha Beach near Namo River) ........ 148 Table 8-32. Beach specific potential source summary (Site S-03: Agat Bay) .......................................... 155 Table 8-33. TMDL summary (Site S-03: Agat Bay) ................................................................................ 157 Table 8-34. Reductions required to meet the TMDL (Site S-03: Agat Bay) ............................................ 157 Table 8-37. Beach specific potential source summary (Site S-17: Togcha Beach at SCA) ..................... 164 Table 8-38. TMDL summary (Site S-17: Togcha Beach at SCA) ............................................................ 166 Table 8-39. Reductions required to meet the TMDL (Site S-17: Togcha Beach at SCA) ........................ 166 Table 8-40. Beach specific potential source summary (Site S-04: Bangi Beach) .................................... 174 Table 8-41. TMDL summary (Site S-04: Bangi Beach) ........................................................................... 176 Table 8-42. Reductions required to meet the TMDL (Site S-04: Bangi Beach) ....................................... 176 Table 8-43. Beach specific potential source summary (Site S-05: Nimitz Beach) ................................... 184 Table 8-44. TMDL summary (Site S-05: Nimitz Beach) ......................................................................... 186 Table 8-45. Reductions required to meet the TMDL (Site S-05: Nimitz Beach) ..................................... 186 Table 8-48. Beach specific potential source summary (Site S-06: Umatac Bay) ..................................... 193 Table 8-49. TMDL summary (Site S-06: Umatac Bay)............................................................................ 195 Table 8-50. Reductions required to meet the TMDL (Site S-06: Umatac Bay) ....................................... 195 Table 8-51. Beach specific potential source summary (Site S-07: Toguan Bay) ..................................... 203 Table 8-52. TMDL summary (Site S-07: Toguan Bay) ............................................................................ 205 Table 8-53. Reductions required to meet the TMDL (Site S-07: Toguan Bay) ........................................ 205 Table 8-54. Beach specific potential source summary (Site S-08: Merizo Pier - Mamaon Channel). ..... 213 Table 8-55. TMDL summary (Site S-08: Merizo Pier – Mamaon Channel) ............................................ 215 Table 8-56. Reductions required to meet the TMDL (Site S-08: Merizo Pier - Mamaon Channel) ........ 215 Table 8-57. Beach specific potential source summary (Site S-09: Inarajan Pool) ................................... 223 Table 8-58. TMDL summary (Site S-09: Inarajan Pool) .......................................................................... 225 Table 8-59. Reductions required to meet the TMDL (Site S-09: Inarajan Pool) ...................................... 225 Table 8-60. Beach specific potential source summary (Site S-10: Inarajan Bay) .................................... 232 Table 8-61. TMDL summary (Site S-10: Inarajan Bay). .......................................................................... 234 Table 8-62. Reductions required to meet the TMDL (Site S-10: Inarajan Bay) ....................................... 234 Table 8-63. Beach specific potential source summary (Site S-11: Talofofo Bay) ................................... 242 Table 8-64. TMDL summary (Site S-11: Talofofo Bay) .......................................................................... 244 Table 8-65. Reductions required to meet the TMDL targets (Site S-11: Talofofo Bay) .......................... 244

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Table 8-66. Beach specific potential source summary (Site S-18: First Beach - Talofofo) ..................... 252 Table 8-67. TMDL summary (Site S-18: First Beach - Talofofo) ............................................................ 254 Table 8-68. Reductions required to meet the TMDL (Site S-18: First Beach - Talofofo) ........................ 254 Table 8-69. Beach specific potential source summary (Site S-12: Ipan Beach) ....................................... 261 Table 8-70. TMDL summary (Site S-12: Ipan Beach) ............................................................................. 263 Table 8-71. Reductions required to meet the TMDL (Site S-12: Ipan Beach) ......................................... 263 Table 8-72. Beach specific potential source summary (Site S-13: Togcha Bay - Talofofo) .................... 271 Table 8-73. TMDL summary (Site S-13: Togcha Bay - Talofofo) ........................................................... 273 Table 8-74. Reductions required to meet the TMDL (Site S-13: Togcha Bay - Talofofo) ...................... 273 Table 8-75. Beach specific potential source summary (Site S-14: Tagachang Beach) ............................ 281 Table 8-76. TMDL summary (Site S-14: Tagachang Beach) ................................................................... 283 Table 8-77. Reductions required to meet the TMDL (Site S-14: Tagachang Beach) ............................... 283 Table 8-78. Beach specific potential source summary (Site S-15: Pago Bay) ......................................... 291 Table 8-79. TMDL summary (Site S-15: Pago Bay) ................................................................................ 293 Table 8-80. Reductions required to meet the TMDL (Site S-15: Pago Bay) ............................................ 293 Table 9-1. Summary of needed reductions to meet the TMDL (Geometric Mean – dry season) ............ 295 Table 9-2. Summary of needed reductions to meet the TMDL (Geometric Mean – wet season) ............ 296 Table 9-3. Summary of needed reductions to meet the TMDL (90th percentile – dry season) ................ 297 Table 9-4. Summary of needed reductions to meet the TMDL (90th percentile – wet season) ................ 298 Table 9-5. Priority beach implementation................................................................................................. 299 Table 9-6. Source categories identified using a duration curve framework. ............................................ 301 Table 9-7. Beach-specific bacteria sources ............................................................................................... 302 Table 9-8. Source-specific implementation opportunities ........................................................................ 303 Table 9-9. Implementation programs highlighted using a duration curve framework. ............................ 304

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Acronyms BMPs CAFO cfs CNMI CNPCP CZARA DMR DOD DPW GCA GCMTF GIS GPA Guam EPA GWA LAs LID Marina Rules and Regulations MDL mL MS4s NPDES POTWs RBMP RWUMP SSOs STP TMDLs USEPA USGS WLAs WPC WQS

Best Management Practices Confined Animal Feeding Operations Cubic Feet Per Second Commonwealth of the Northern Mariana Islands Coastal Nonpoint Control Program Coastal Zone Act Reauthorization Amendments Discharge Monitoring Report Department of Defense Department of Public Works Guam Code Annotated Guam Civilian / Military Task Force Geographic Information System Guam Power Authority Guam Environmental Protection Agency Guam Waterworks Authority Load Allocations Low Impact Development Marina Rules and Regulations of the Port Authority of Guam Minimum Detection Limit Milliliters Municipal Separate Storm Sewer Systems National Pollutant Discharge Elimination System Publicly owned treatment works Recreational Beach Monitoring Program Recreational Water Use Management Plan Sanitary system overflows Sewage Treatment Plant Total Maximum Daily Loads United States Environmental Protection Agency U.S. Geological Survey Waste Load Allocations Water Pollution Control Water Quality Standards

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1. Overview Data collected through Guam’s Recreational Beach Monitoring Program (RBMP) has served as the basis to place a number of locations on their §303(d) list. Guam’s Integrated Report indicates that a priority action is to work towards developing Total Maximum Daily Loads (TMDLs) for impaired Tier 1 beaches. This TMDL report summarizes information for 16 beaches located in the SouthernGuam Watershed and nine beaches located along the southeast coastline of the Northern Watershed and describes the approach used to develop TMDLs for these impaired waters. These 25beaches, identified in Table 1-1, are listed as impaired due to exceedances of Guam’s Water Quality Standards for enterococci bacteria and are referred to as the TMDL project area or TMDL beaches throughout this report.

Table 1-1. Waterbodies covered under the Bacteria TMDLs for Twenty-five Guam Beaches Waterbody ID

Name

Impairment

Marine Water Category

N-21

Adelup Beach Park

Enterococci

M-2

N-22

Adelup Point Beach (West of Adelup Park)

Enterococci

M-2

N-14

Asan Bay Beach

Enterococci

M-2

N-15

Piti Bay

Enterococci

M-2

N-16

Santos Memorial Park Beach

Enterococci

M-2

N-17

United Seamen's Service

Enterococci

M-2

N-20

Port Authority Beach

Enterococci

M-3

N-18

Outhouse Beach

Enterococci

M-3

N-19

Family Beach

Enterococci

M-2

S-02

Togcha Beach - Namo

Enterococci

M-2

S-03

Togcha Beach - Agat Bay

Enterococci

M-2

S-17

Togcha Beach - Beach at Southern Christian Academy

Enterococci

S-04

Bangi Beach

Enterococci

M-2

S-05

Nimitz Beach

Enterococci

M-2

S-06

Umatac Bay

Enterococci

M-2

S-07

Toguan Bay

Enterococci

M-2

S-08

Merizo Pier - Mamaon Channel

Enterococci

M-2

S-09

Inarajan Pool

Enterococci

M-2

S-10

Inarajan Bay

Enterococci

M-2

S-11

Talofofo Bay

Enterococci

M-2

S-18

First Beach - Talofofo

Enterococci

M-2

S-12

Ipan Beach

Enterococci

M-2

S-13

Togcha Bay - Talofofo

Enterococci

M-2

S-14

Tagachang Beach

Enterococci

M-2

S-15

Pago Bay

Enterococci

M-2

These TMDLs will address the enterococci impairments. The report begins with a short summary of the setting and general water quality concerns including applicable standards (Sections 2 and 3, respectively). An important part of TMDL development is to build on existing knowledge. This involves a review and

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

analysis of data collected from project area beaches (Section 4). Included are groupings for beach TMDLs based on location, physical characteristics, and potential sources (Section 5). Potential sources that affect water quality at RBMP sites are summarized and TMDL allocations are provided (Sections 6 through 8). These TMDLs use a hydrology-based framework, combining RBMP data with flow and precipitation information. This provides an expanded analysis of the monitoring data, which allows patterns to be examined, based on estimates of flows conditions (e.g., wet versus dry). Knowledge of conditions most likely to cause water quality problems supports a meaningful transition to implementation efforts (Section 9).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

2. Setting Guam has a tropical oceanic climate with warm temperatures and high humidity. The subtropical weather allows for year-round recreation at all beaches. The majority of recreational activity occurs along stretches of sandy beaches or limestone plateauseasily accessible from the shore that are classified as “M2 waters” or “Good” under Guam’s Water Quality Standards (Section 3). Data have been provided from 25 RBMP stations for the purpose of developing bacteria TMDLs. These sites are situated along Guam’s Northern and SouthernWatershed shorelines (Figure 2-1). Basic station information is summarized inTable 2-1. The stations are grouped by the major water where they are located (e.g., Asan Bay, Agat Bay, West Hagåtña Bay). Information from the RBMP has been the basis for issuing health advisories at project area beaches, as well as including these waters on Guam’s §303(d) list. Potential causes include wastewater-related sources (septic systems, sewer line breaks, sanitary sewer overflows, treatment plant discharges), stormwater (surface runoff from developed land, roads, construction areas), and recreation-related sources (marinas, boat discharges).

Figure 2-1. Location of Guam TMDL project area beaches

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 2-1. Guam TMDL project area beaches Village

Water

Beach

Shore Access (miles)

N-21

Adelup Beach Park

Hagåtña

West Hagåtña Bay (Agana River to Fonte River)

Beach at Fonte River, West HagåtñaBay

0.13

Adelup Park

N-22

Adelup Point Beach (West of Adelup Park)

Asan

West Hagåtña Bay

West of Adelup Point, Asan Bay

0.41

Adelup Park

N-14

Asan Bay Beach

Asan

Asan Bay

0.53

War In The Pacific National Historical Park

N-15

Piti Bay

Piti

Piti Bay

N-16

Santos Memorial Park Beach

Piti

Piti Bay

N-17

United Seamen's Service

Site ID

Station Name

N-20 N-18

Port Authority Beach Outhouse Beach

Piti

Piti Bay

Piti

Apra Harbor

Piti

Apra Harbor

Asan Memorial Beach, Head of Asan Bay Beach at Piti Bay (Tepungan Beach)

1.08

Pedro Santos Park United Seamen's Service Beach (USO Beach) Port Authority Beach Outhouse Beach

0.52

0.46

Family Beach

Piti

Apra Harbor

Family Beach

0.15

S-02

Togcha Beach - Namo

Agat

Agat Bay

Togcha Beach aka Agat Beach

0.79

Agat

Agat Bay

Agat

Agat Bay

S-17

Togcha Beach - Agat Bay Togcha Beach - Beach at SCA

S-04

Bangi Beach

Agat

Agat Bay

Beach South of Finile River

1.17

S-05

Nimitz Beach

Agat

Taleyfac Bay

Nimitz Beach

0.49

S-06

Umatac Bay

Umatac

Umatac Bay

Head of Umatac Bay

0.14

S-07

Toguan Bay

Merizo

Toguan Bay

0.46

S-08

Merizo Pier Mamaon Channel

Merizo

Cocos Lagoon (Mamaon Channel)

Merizo Public Pier Park

0.46

S-09

Inarajan Pool

Inarajan

Inarajan Pools

0.07

S-10

Inarajan Bay

Inarajan

Inarajan Bay

S-11

Talofofo Bay

Inarajan/ Talofofo

Talofofo Bay

S-18

First Beach Talofofo

Talofofo

Beach at Asanite Point (Talofofo)

Beach at Inarajan Bay Head of Talofofo Bay First Beach

Hoover Park

0.46

N-19

S-03

Features

Agat Small Boat Harbor Fort Santo Angel, Umatac Bay Park

Youth Center, Merizo Pier Park

0.46

Gef Pago Cultural Village

0.21

Talofofo Beach Park

0.06

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Site ID

Station Name

Village

Water

S-12

Ipan Beach

Talofofo

Mana Bay

Yona

Togcha Bay

Yona

Tagachang Beach

Yona/Chalan Pago Ordot

Pago Bay

S-13 S-14 S-15

Togcha Bay Talofofo Tagachang Beach Pago Bay

Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park Beach at Pago Bay

Shore Access (miles) 0.3

Features

Ipan Beach Park

0.27 0.07

Tagachang Beach Park

0.96

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

3. Applicable Water Quality Standards Criteria have been developed that form the basis of Guam’s beach advisory program. These criteria are based on the applicable water quality standards (WQS). Guam’s waterbodies are classified into categories based on designated uses. These categories for marine waters are M-1 / Excellent (whole body contact recreation), M-2 / Good (whole body contact recreation) and M-3 / Fair (limited body contact recreation) (Guam EPA 2001). All but two of the beaches in the TMDL project area are classified as M-2. Outhouse Beach (N-18) and Port Authority Beach (N-20) are classified as M-3 (Table 1-1). The applicable standards for whole body contact recreation and the rationale supporting the criteria are described in Recreational Beach Monitoring Plan: Guam Coastal Waters (Guam EPA 2003). Guam uses the enterococci bacterial indicator to establish criteria that protect for contact recreational uses (in count of bacteria per 100 milliliters [mL]). For M-1 and M-2waters, Guam’s water quality standards (Guam EPA 2001) state that: “Concentrations of enterococci bacteria shall not exceed 35 enterococci/100 mL based upon the geometric mean of five (5) sequential samples taken over a period of thirty (30) days. No instantaneous reading shall exceed 104 enterococci/100 mL”. For M-3 waters, Guam’s water quality standards state that: “Concentrations of enterococci bacteria shall not exceed 35 enterococci/100 mL based upon the geometric mean of five (5) sequential samples taken over a period of thirty (30) days. No instantaneous reading shall exceed 276 enterococci/100 mL”. Recreational swimming and wading occurs year round on Guam’s beaches. Guam Environmental Protection Agency(Guam EPA) issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100mL or a geometric mean concentration of 35 MPN/100mL, over a five week period (note: these concentrations are consistent with the WQS for M-2 waters). Advisory procedures are described in the RBMP Plan (Guam EPA 2003). Guam’s 2010 Integrated Report indicated that for calendar year 2008, 762 swimming advisories were issued, while in calendar year 2009, 752 swimming advisories were issued. West Hagåtña Bay was closed for a full year in 2009 while a sewage leak from the Hagåtña Sewage Treatment Plant (STP) was being treated (Guam EPA 2010, Tables B7a-d and B8a-d, Appendix B).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

4. Water Quality Data An important step in the TMDL development process is the review of water quality conditions, particularly data and information used to list segments. Examination of water quality monitoring data is a key part of defining the problem that these TMDLsare intended to address. This section provides a brief review of available water quality information including a summary of the spatial distribution for the bacteria monitoring data based on Geographic Information System (GIS) analyses. The discussion also considers seasonal patterns and trends to help identify potential analytical methods that can strengthen the TMDL development process for the impaired beaches.Summary of all the water quality information is presented in Section 4.1 and Section 4.2, while trends and data analyses methods are discussed using an example beach in Section 4.3 through Section 4.5. Similar analyses are performed for each beach in the Individual Beach Assessments and TMDLs section (Section 8).

4.1. Available Information The importance of Guam’s beaches for water contact recreation has provided long standing support for the RBMP. Data have been collected by Guam EPA under this program for over 20 years. As a result of the Beach Act, an inventory of 113 beaches was conducted. Of these, 73 were prioritized into three tiers. Tier 1 includes beaches that are easily accessible, highly visited, characterized by a high number pollution sources, and require frequent monitoring. Guam’s RBMP monitoring stations identified in Table 2-1 are all classified as Tier 1. Bacteria monitoring data collected weekly from these sites are reported in terms of bacteria counts per 100mL. These data are used to make beach advisory decisions, as well as to assess status and trends. Table 4-1 provides an inventory of the TMDL beaches sampled for the past 11 years starting in 2001.

Table 4-1. Inventory of Bacteria TMDL monitoring data (2001-2011) Data Coverage (year)

Station ID

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Station Name

N-21

Adelup Beach Park

•

N-22

Adelup Point Beach (West of Adelup Park)

•

N-14

Asan Bay Beach

•

N-15

Piti Bay

•

N-16

Santos Memorial Park Beach

•

N-17

United Seamen's Service

•

N-20

Port Authority Beach

•

N-18

Outhouse Beach

•

N-19

Family Beach

•

S-02

Togcha Beach - Namo

•

S-03

Togcha Beach - Agat Bay

•

S-17

Togcha Beach - Beach at SCA

•

S-04

Bangi Beach

•

Bacteria Total Maximum Daily Loads

Data Coverage (year) 2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Station Name

2001

Station ID

Twenty Five Guam Beaches

S-05

Nimitz Beach

•

S-06

Umatac Bay

•

S-07

Toguan Bay

•

S-08

Merizo Pier - Mamaon Channel

•

S-09

Inarajan Pool

•

S-10

Inarajan Bay

•

S-11

Talofofo Bay

•

S-18

First Beach - Talofofo

•

S-12

Ipan Beach

•

S-13

Togcha Bay - Talofofo

•

S-14

Togcha Bay - Talofofo

•

S-15

Pago Bay

•

4.2. Spatial Distribution Sites included in this TMDL represent an array of settings. Each site has a unique set of features, sources of bacteria, and varying conditions affecting transport mechanisms. A logical starting point for developing these beach TMDLs is to examine the spatial distribution of enterococci concentrations using the RBMP information. Based on 2001 and 2011data downloaded from USEPA’s BEACON 2.0 notification system, the frequency of beach advisories for each beach from due north (West Hagåtña Bay) to the northeast (Pago Bay) (moving counterclockwise around the island) is displayed in Figure 4-1 (USEPA, 2012).While beach advisories occur throughout the TMDL project area, the most beach advisories occurred at Piti Bay (N-15) with 90 percent advisories. A trend of high advisory frequencies is also evident along the southern coastline from Agat to Talofofo Bays (S-03 to S-11) where beach advisory frequencies range from 40 to 80 percent. Figure 4-2 provides a summary of the data distribution for each beach over the same period using the box and whisker format. The box and whisker format allows analysis of general patterns by displaying the data distribution. The top of the whisker is the max, i.e. one hundred percent of all data are at or below that level. The box depicts the 75th percentile (top) and the 25th percentile (bottom). Half of all observed values fall within this range. The line through the box is the median (or 50th percentile), while the bottom of the whisker represents the minimum observed data. The monitoring data presented in Figure 4-2 show that each RBMP beach site had maximum observed concentrations that exceeded the instantaneous WQS of 104 counts/100 mL by at least one order of magnitude. Despite these significant concentrations, several beaches had a generally low range of bacteria concentrations where 75 percent of samples did not exceed 10 counts/100 mL.On the other hand, a number of other beaches demonstrated significant exceedances where 75 percent of all samples from 2001 through 2011 were above the instantaneous WQS.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 4-1. Spatial distribution of beach advisories

Figure 4-2. Spatial distribution of beach monitoring data 9

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Spatial representations of bacteria concentrations at the beach sites are shown in Figure 4-3 and Figure 4-4. The 90th percentile concentration and average rolling geomean based on the entire period of record from 2001 through 2011 were compared against their respective instantaneous and geomean WQSs for each beach in Figure 4-3 and Figure 4-4, respectively. As shown in both figures, sites in Apra Harbor and three sites along the eastern coast of southern Guam (S-12, S-14, and S-18) do not have a serious issue of exceeding water quality standards. The most critical sites where concentrations are well above the water quality standards include Bangi Beach (S-04), Toguan Bay (S-07), and Talofofo Bay (S-11).

Figure 4-3. 90th percentile bacteria concentrations at each beach monitoring site

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 4-4. Average rolling geomean for each beach monitoring site

4.3. Annual Analysis An annual analysis is useful in looking for trends at specific sites where efforts to address beach advisories have been implemented. The 2010 Integrated Report describes several programs and planned watershed assessments targeting water quality improvement at recreational beaches (Guam EPA 2010).Figure 4-5 presents a year-by-year summary of the RBMP data at an example project area monitoring site, Togcha Bay (S-13). This provides a useful way to examine trends at each site relative to both central tendency and annual variation. This visual analysis can be used as a means to evaluate a programâ&#x20AC;&#x2122;s effectiveness in improving water quality over time (i.e., decreasing trends in bacteria concentrations show improvements over time).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 4-5. Annual analysis for Togcha Bay

4.4. Seasonal Variation For TMDL development, water quality analysis must consider temporal (e.g., seasonal or inter-annual) variations in discharge rates, receiving water flows, and effects on designated uses. These considerations are particularly important because point and nonpoint sources can discharge at different rates during different time periods (see United States Environmental Protection Agency [USEPA] Pathogen Protocol for more detail; USEPA 2001). Seasonal changes often relate to typical amounts of rainfall. In Guam, the wet season normally extends from July to December and dry season from January to June. Annual average rainfall varies from about 110 inches in the higher areas to about 80 inches along the shores. Although rainfall primarily drives the hydrology of an area, other discharges influence the flow in streams, rivers, and outlets to bays, estuaries, and beaches. Therefore, the study of stream flow helps characterize hydrologic conditions that can be driven by both point and nonpoint sources. The following sections present several analytical methods used to examine seasonal patterns and trends that can strengthen the TMDL development process. The assessment of seasonal trends in bacteria data and in stream flow data are presented in Section 4.4.1 and Section 4.4.2, respectively.

4.4.1. Seasonal Patterns in Water Quality Monitoring Data While general patterns may be apparent, a noticeable amount of variability is expected in bacteria beach monitoring data. Some of this variability is likely attributed to different source areas that affect each site as well as the influence of seasons. Trends are often observed when comparing data for wet and dry seasons. Variability within these seasons can be attributed to the frequency and magnitude of rainfall events as well as localized sources. For instance, samples taken during the dry season could coincide with rainfall events. This would result in measured bacteria concentrations that reflect wet-weather

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Twenty Five Guam Beaches

sources(e.g., stormwater issues), despite having occurred during a dry season month. Linkages to potential sources are further discussed in Section 6. Figure 4-6 depicts an example of seasonal patterns at one of the project area monitoring sites, Togcha Bay (S-13). Significant variability in bacteria concentrations is illustrated by the large whiskers on the monthly boxplots. Although variability is evident every month, the month to month central tendency increases as data are collected from the dry season months and into the wet season months. As illustrated, higher monthly medians are observed during the wet months compared to the dry months where the medians fall below 35 counts/100 mL (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented can be compared with the instantaneous WQS).

Figure 4-6. Seasonal variation at Togcha Bay Methods exist to improve the analysis of wet- versus dry-weather patterns. One option is to display concentration measurements against hydrologic conditions. Flow gages can provide hydrologic conditions in terms of surface runoff and stream flow that would be relative to each examined site.

4.4.2. Stream Flow and Seasonal Variation Heavy rainfall events leading to surface runoff or storm drain issues influence water quality at beaches. Excessive runoff or stormwater issues such as overflows, leaks, or untreated stormwater runoff can introduce land-based bacteria to receiving waters. Guam EPA has identified beaches that receive additional monitoring after a rainfall event greater than two inches in a 24-hour period. Four beaches addressed in this TMDL are monitored in this manner (Santos Memorial Park Beach [N-16], Toguan Bay [S-07], Inarajan Bay [S-10], and Talofofo Bay [S-11]) according to the 2003 Guam RBMP monitoring plan. At beaches with a close proximity to storm drains, signs are posted advising the public of the risks associated with elevated bacteria levels during periods of heavy rainfall.

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Water quality parameters can be related to stream flow rates to assess the influence of rainfall and stormwater on receiving water quality. Relating stream flow rates to water quality parameters is useful in identifying the conditions under which exceedances occur and any seasonal patterns that may exist. Seasonal variation in flow can be a key part of TMDL development. Routine flow monitoring of storm runoff has not been conducted at all sites in the project area. However, flow information from nearby sites can be used as an indicator of general hydrologic conditions when water quality samples were taken. In southern Guam, the U.S. Geological Survey (USGS) operates several inland flow gages. Assignments of USGS gages to beach monitoring sites are presented in Table 4-2. These assignments are based on completeness of flow dataset, evaluation of the drainage areas, and precipitation patterns. Figure 4-7 illustrates the location of these select USGS gages relative to beach monitoring stations and annual rainfall distribution. The assigned flow gage was used to evaluate hydrologic conditions associated with each sampling event.

Table 4-2. Water quality stations and USGS flow gages Field ID

Field Site Name

N-21

Adelup Beach Park

N-22

Adelup Point Beach (West)

N-14

Asan Bay

N-15

Piti Park

N-16

Santos Memorial Park

N-17

United Seaman's Service

N-18

Outhouse Beach

N-19

Family Beach

N-20

S-04

Port Authority Beach Togcha Beach (near Namo River) Togcha Beach (Agat Park Beach) Togcha Beach (near Southern Christian Academy) Bangi Beach

S-05

Nimitz Beach

S-06

Umatac Bay

S-07

Toguan Bay

S-08

Merizo Pier

S-09

Inarajan Pool

S-10

Inarajan Bay

S-11

Talofofo Bay

S-18

First Beach (Ipan Point Beach)

S-12

Ipan Beach

S-13

Togcha Bay

S-14

Tagachang Beach

S-15

Pago Bay

S-02 S-03 S-17

USGS Flow Gage

Flow Station Location

Flow Data Coverage for Study Period (%)

Flow Gage Drainage 2 Area(mi )

16865000

Pago River near Ordot, Guam

80.7

5.57

16807650

Aplacho River at Apra Heights, Guam

84.1

0.44

16809600

La Sa Fua River near Umatac, Guam

100

1.03

16848100

Almagosa River near Agat, Guam

100

1.33

16865000

Pago River near Ordot, Guam

80.7

5.57

Note: For the gages without 100 percent coverage, a rainfall-runoff watershed model was used to fill in flow data gaps and provide a more comprehensive flow dataset (see Tetra Tech 2012).

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Figure 4-7. Location of USGS gaging stations and annual rainfall distribution Relationships between bacterial levels and hydrologic conditions can be further explored by assessing for seasonal variation. A seasonal analysis on the flow data for all the USGS gages confirms a seasonal pattern consisting of a wet season and dry season. For Guam, the wet season months occur between July

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and December; whereas the dry season months occur between January and June. The months on either end of these seasons show the transition in flow conditions. Seasonal variation of flow for each gage based on the available USGS flow data is illustrated in Figure 4-8 throughFigure 4-11.

Figure 4-8. Seasonal variation of flows for the Pago River

Figure 4-9. Seasonal variation of flows for the AplachoRiver

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Figure 4-10. Seasonal variation of flows for the La Sa Fua River

Figure 4-11. Seasonal variation of flows for the Almagosa River In many cases, the flow record is not entirely complete (see Flow data coverage column in Table 4-2). To utilize the full extent of water quality data (i.e., for water quality samples without a corresponding flow

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value), a rainfall-runoff watershed modelwas used to fill in flow data gaps and provide a more comprehensive flow dataset for use in the individual beach assessments and TMDLs (Section 8) (see Tetra Tech 2012 for more details on the watershed model).

4.5. Duration Curve Analyses A duration curve framework looks at the cumulative frequency of historic water quality and flow data over a specified period. A duration curve relates the water quality or flow values to the percent of time those values have been met or exceeded, providing a uniform scale ranging between 0 and 100. Thus, the full range of values is considered. Low values are exceeded a majority of the time, while higher values are exceeded infrequently (USEPA 2007).Hydrologic conditions for an example gage in southern Guam are explored through the use of a flow duration curve andare discussed in Section 4.5.1. Temporal and hydrologic trends are conjointly examined through water quality duration curves, discussed in Section 4.5.2 (note: detailed analyses for each beach are presented in Section 8).

4.5.1. Flow Duration Curves Flow duration curves provide a way to address the inherent variability associated with hydrologic information (e.g., seasonal variation, year-to-year variation). Flow duration analysis looks at the cumulative frequency of historic flow data and plots observed flows with their relative percent exceedances or flow duration interval (%). The analysis results in a curve (flow duration curve), which describes the percentage of time during which specified flows are equaled or exceeded (Leopold 1994). Low flows are exceeded a majority of the time, whereas floods are exceeded infrequently. Duration curves provide the benefit of considering the full range of flow conditions. Development of a flow duration curve is based on daily average stream discharge data. A typical curve runs from high flows to low flows along the x-axis, as illustrated inFigure 4-12 for the Almagosa River. High flows fall within the 0-10 percent flow duration interval where 10 percent of observed flows equal or exceed 14 cubic feet per second (cfs). Low flows, on the other hand, fall within the 90-100 percent flow duration interval where 90 percent of observed flows equal or exceed 0.46 cfs. These flow duration intervals are relative and will vary between flow gages due to varying hydrologic conditions. Flow duration curve intervals can be grouped into several broad categories or zones. These zones provide additional insight about conditions and patterns associated with the impairments. A common way to look at the duration curve is by dividing it into five zones, as illustrated inFigure 4-12: one representing high flows(0-10%), another for moist conditions (10-40%), one covering mid-range flows (40-60%), another for dry conditions (60-90%), and one representing low flows (90-100%). This particular approach places the midpoints of the moist, mid-range, and dry zones at the 25th, 50th, and 75th percentiles respectively (i.e., the quartiles). The high zone is centered at the 5th percentile, while the low zone is centered at the 95th percentile.

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Figure 4-12. Flow duration curve for Almagosa River Gage (USGS Gage 16848100)

4.5.2. Water Quality Duration Curves Ambient monitoring data, taken with some measure or estimate of flow at the time of sampling, can be used to develop water quality duration curves. Water quality duration curves plot the water quality value of a sample against the relative percent exceedance of the corresponding flow measurement. Displaying ambient water quality data and the daily average flow on the date of the sample (expressed as a flow duration curve interval),characteristics can be drawn to describe the water quality impairment. Values that plot above the criterion or numeric target indicate an exceedance of the water quality criterion, while those below the load duration curve show compliance. The impairment can be examined to see if it occurs across all flow conditions, corresponds strictly to high flow events, or conversely, only to low flows. Impairments observed in the low flow zone typically indicate the influence of continuous, point sources (including leaky sewer lines, failing septic systems, and untreated sewage discharges), while those in high flow zones generally reflect potential nonpoint source contributions often associated with stormwater runoff (Section 6). This concept is illustrated in Figure 4-13.

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Figure 4-13. Water quality duration analysis for Togcha Bay In this example (Figure 4-13), Togcha Bay experiences the most elevated bacteria concentrations and exceedances under high flow conditions. Although the geomeans of other flow regimes remain below the instantaneous WQS, variability in the sampling has resulted in occasional exceedances as shown by the high maximum observed concentrations. These samples can be characterized beyond flow regime to examine the root of these exceedances and elevated concentrations. The utility of duration curve zones for pattern analysis can be further enhanced to characterize wetweather concerns by identifying samples taken during wet season and runoff events. For example, Figure 4-14 uses a â&#x20AC;&#x153;+â&#x20AC;? to identify those samples collected during the wet season (July â&#x20AC;&#x201C; December).Runoff events are identified by comparing the flow the day the sample was collected with the flow on the preceding day. In reviewing measurements, rapid increases in daily average flow can serve as indicators of storm events. Any one-day increase in flow greater than 0.1mm where baseflow is less than 50 percent is assumed to be the result of surface runoff due to a storm event. In Figure 4-14, these runoff event samples are identified with a shaded diamond. In a detailed water quality duration analysis (Figure 4-14), classifying seasonal or runoff events across all flow regimes provides insight on the potential causes surrounding the observed bacteria concentration. Note, data less than 10 counts/100 mL are not presented in detailed water quality duration analysis figures (Figure 4-14) as 9 counts/100 mL is the minimum detection limit (MDL) and the plots are considerably clearer to evaluate when showing 10 counts/100mL or more.

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Figure 4-14. Detailed water quality duration analysis for Togcha Bay Figure 4-13 and Figure 4-14 illustrate the utility of water quality duration curves in assessing Guam’s RBMP data for Togcha Bay. As shown, most exceedances occur under high flow conditions with elevated bacteria levels continuing to occur under moist flow conditions (Figure 4-13). The detailed analysis (Figure 4-14), confirms that the highest bacteria levels are generally associated with storm events (indicated by the shaded diamonds) and/or occur during the wet season (indicated by the “+” markers). Limited exceedances under dry season, dry flow conditions may be indicative of continuous point sources such as leaky sewer lines or failing septic systems. These dry weather sources and delivery mechanisms warrant further investigation. In Togcha Bay, however,Figure 4-14 confirms that bacteria levels are highest during high flow conditions, suggestive of stormwater runoff sources and wet-weather issues. Water quality duration curves can be further used to evaluate variability issues relative to dry and wet seasons.Wet season events are typically affiliated with highest flow conditions as the season is marked by heavy and frequent rainfalls leading to increased stream flow. The dry season, on the other hand, represents conditions when stream flow is low and dominated by baseflow. Comparing seasonal observations across all flow regimes assists in connecting observed conditions to potential sources. The connection of seasonal trends to potential sources is discussed in Section 6. A water quality duration curve emphasizing seasonal influences is illustrated in Figure 4-15 where wet- and dry-season data are separated out for each flow regime.

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Twenty Five Guam Beaches

Figure 4-15. Wet versus dry seasonal duration curve analysis for Togcha Bay Similar to Figure 4-13and Figure 4-14, the seasonal comparison (Figure 4-15) confirms that Togcha Bay has the highest concentrations and most exceedances under high flow conditions, but emphasizes that these observations are mostly wet-season events. For Togcha Bay, dry season observations are often not significant, shown by the low dry season geomeans across all flow regimes. The seasonal comparison demonstrates that significant exceedances observed at Togcha Bay are driven by wet-season events that may be attributed to stormwater issues such as untreated stormwater runoff. Less frequent exceedances observed during the dry season can also be attributed to the infrequent rainfall events following long periods of no rain.

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5. Source Assessment Source assessments are an important component of water quality management plan and TMDL development. These analyses are generally used to evaluate the type, magnitude, timing, and location of pollutant loading to a waterbody (USEPA 1999). Source assessment methods vary widely with respect to their applicability, the ease of use, and acceptability. This section contains a general discussion of potential bacteria sources to the TMDLbeaches, while the individual beach assessments presented in Section 8 describe sources specific to each impaired beach. Assessment reports prepared by Guam EPA have identified a number of pollution threats to these beaches. Included are concerns such as stormwater runoff, sewer line blockages and breaks, point source effluents, sanitary system overflows, septic systems, marina and recreational boating, debris and bottom deposits, and seeps connected to stormwater ponding basins. For purposes of this assessment, potential sources have been grouped into three general categories that include: • Waste Water • Stormwater • Recreation and Other The intent of these groupings is two-fold. The first is to examine potential source area and delivery mechanisms. This supports informed decisions regarding the most appropriate technical approach for connecting water quality data to TMDL targets. For example, stormwater sources are driven by rainfall and the resultant runoff. Elevated bacteria levels under high flow conditions reflect this pattern where stormwater is a significant source.The second reason for grouping categories is to align sources in a way that looks ahead to those water quality management programs and implementation efforts best suited to address the problems. Several of these sources also address methods of pollutant transport (e.g., stormwater, sewer mains, effluent, etc.). In addition, the geology of the Southern Watershed affects pollutant delivery. The geology changes from one side of the island to the other (Figure 5-1). Volcanic and alluvium and beach deposits are prevalent on the western side, while limestone dominates the shoreline areas along the eastern coastline. As described in beach assessments presented in Section 8, local geology can affect the transport of water and associated pollutants; therefore, it is included in the pollutant source maps.

5.1. Waste Water Sources This group includes those sources associated with the generation, conveyance, treatment, and discharge of domestic and industrial wastewater. Potential threats identified in Guam EPA assessments are: • • • • •

Septic systems (Figure 5-1) Sewer line blockages and / or breaks Sanitary system overflows (SSOs) Publicly owned treatment works (POTWs) Industrial point sources (e.g.,Guam Power Authority [GPA] effluent)

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Figure 5-1. Location of non-sewered buildings in the TMDL project area Domestic wastewater associated with population increase is the largest potential source of pollution to all waters of Guam (Guam EPA 2006). There are a number of potential opportunities for wastewater sources to contribute bacteria to recreational beach waters. Transport and delivery mechanisms include:

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Twenty Five Guam Beaches

• Groundwater transport of leachate from failed septic systems either directly or indirectly to coastal waters • Leaking from blockage or breakage of sewerage mains that result in either direct or indirect discharge to coastal waters • Inadequate treatment or lack of disinfection from POTWs These processes tend to be more common in areas with higher population densities, such as residential or commercial zones. Due to economic difficulties, development in many areas has occurred without adequate sewage infrastructure. As a result, a number of residential and commercial buildings depend on septic tanks and leaching field systems for waste disposal. Guam EPA has identified buildings in the TMDL project area that are not sewered through GIS data layers (Figure 5-1). Residential septic systems treat human wastes using a collection system that discharges liquid wastes into the soil through a series of distribution lines that comprise the drain field. Bacteria naturally die-off as the effluent percolates through the soil to groundwater. Septic systems are designed to effectively remove bacteria when properly installed and maintained. A septic system failure occurs when there is a discharge of waste to the soil surface where it becomes available for washoff into surface waters (both directly or indirectly through the network of storm drains and ditches). Failing septic systems can deliver high bacteria loads to surface waters, depending on the proximity of the discharge to drainage systems and the timing of opportunities for pollutant delivery (e.g., rainfall events). Septic system failures typically occur in older systems that are not adequately maintained with periodic pump outs. In more densely populated areas, residential and commercial buildings have been connected to wastewater collection systems. Efforts to phase out septic systems has resulted in reduced bacteria loads from these sources. However, portions of the collection system suffer from sewer line blockages or breaks. This results in SSOs or direct discharge to coastal waters. SSOs and sewer line breaks can also result in indirect discharge to coastal waters by conveyance through the storm drainage or ditch network. Table 5-1 summarizes SSO overflows in the TMDL area from September 2011 through December 2011. In this four month span of time, there were seventeen reported wastewater spills totaling 4,254 gallons of wastewater. Also during that time there were two WWTP bypasses releasing 2,512,350 gallons of wastewater through the WWTP SSO system.

Table 5-1. Reported SSOs that may affect TMDL Beaches (September to December 2011) Village

Potential Beach Affected

Number of Spills

Net Spill Volume (Gallons)

Asan

N-14, N-15

2,184

Hagåtña

N-21, N-22

1,800

Sta. Rita

S-02, S-03, S-17

Umatac/Merizo

S-07

Inarajan

S-09 and S-10

100

Yona

S-14

130

# of WWTP Bypasses

Net Volume Bypass (Gallons)

2,512,350

Several point sources with NPDES permits discharge in areas that may affect water quality at the TMDL beaches (Table 5-2). The Guam Waterworks Authority (GWA) owns and operates fourwastewater

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treatment facilities (also called sewage treatment plants [STP]) that affect these TMDL waters and the US Navy operates one STP, shown inFigure 5-2.In addition, the Guam Shipyard has four outfalls permitted to discharge bacteria to Apra Harbor. Other industrial permits are present in the watershed but are not included in the TMDL as they do not discharge bacteria. Two additional WWTP are currently not permitted and it is assumed they are not affecting the TMDL waters (Table 5-3). GWA is currently under a Stipulated Order to address several problems that contribute to beach advisories. Included in the Order are renovations and upgrades to the WWTPs, as well as actions to correct problems associated with portions of the conveyance system. Permitted facilities identified in Table 5-2 will receive waste load allocations (WLAs). The Government of Guam will receive load allocations (LAs) to address nonpoint sources.

Table 5-2. Point sources with NPDES permits that may affectthe TMDL beaches

NPDES ID

Discharger

Facility Name

Receiving Water

GU0020222

Guam Waterworks Authority

Agat-Santa Rita STP

Agat Bay (Philippine Sea)

GU0020095

Guam Waterworks Authority

Baza Gardens STP

Mana Bay (North Pacific Ocean)

GU0020273

Guam Waterworks Authority

Umatac/Merizo STP

Toguan Bay (Philippine Sea)

GU00200087

Guam Waterworks Authority

Agana/Hagåtña STP

GU0110019

US Navy

Apra Harbor WWTP

Tipalao Bay (Philippine Sea)

GU0020362

Guam Shipyard

Apra Harbor

Hagåtña Bay (Philippine Sea)

Permittee is also assigned a WLA in the Guam Northern Watershed Bacteria TMDLs (USEPA and Guam EPA 2009).

Table 5-3. Point sources without NPDES permits that may affect the TMDL beaches Facility Permit Excusal Description No Permit (Aeration not operating) No Permit (Effluent Disposal through percolation)

Facility Name Pago Socio STP Inarajan STP

Receiving Water Pago Bay (North Pacific Ocean) Inarajan Bay (North Pacific Ocean)

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Figure 5-2. Location of pump stations and bacteria-discharging permitted facilities

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5.2. Stormwater Sources This group includes those sources associated with bacteria delivered to the TMDLrecreational beach waters as a result of stormwater runoff. All Guam Municipal Separate Storm Sewer Systems (MS4s) are designated for NPDES permitting. MS4 permits covering the entire island of Guam are forthcoming and are expected to be issued by late 2012 or mid-2013. This TMDL will be incorporated into the permits for the relevant drainage areas.Potential threats identified in Guam EPA assessments are: • • • • •

Stormwater runoff (nonpoint source) Stormwater runoff (associated with permitted areas) Highway / road / bridge runoff Highway maintenance and runoff Construction

Urban areas are generally characterized by higher percentages of impervious land due to conversion of natural surfaces to pavement, concrete, and buildings (Figure 5-3). Higher percentages of impervious area, if not properly managed, result in greater surface runoff due to the reduced ability of water to infiltrate into the ground during rain events. As water flows across the land and paved surfaces, debris and pollutants such as bacteria are entrained. Bacteria subsequently flow with the water into storm drains and ditches that lead to local coastal waters. Harmful bacteria and viruses carried by runoff from developed land to local waters can threaten human health and contribute to recreational beach closures. Studies have shown that bacteria levels are typically high in urban runoff (USEPA 2001). Bacteria delivered to coastal waters from developed land may be a significant source of pollution to the TMDLbeaches.

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Figure 5-3. Location of impervious surface in theTMDL project area

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5.3. Recreation and Other Sources This group includes sources related to recreational activities and other concerns that could deliver bacteria to Guam’s recreational beaches. Potential threats identified in Guam EPA assessments are: • • • • • •

Marina and recreational boating Boat discharges Recreation and tourism activities Debris and bottom deposits Contaminated sediments Spills

Unsolicited discharge of untreated wastewater to coastal beaches can occur from recreational sources, notably boats and marinas. Moored boats may be transient and may not pose a constant threat to water quality. Frequency of use in the area and number of boats that may discharge their holding tanks directly to coastal waters are major factors that affect the pollution threat from these sources. Bacteria discharges from boats in marinas may have a more significant effect on coastal waters based on their sheltered locations and reduced freshwater and tidal inflows. Figure 5-4 shows the location of a major marinas identified in Guam EPA GIS data files.

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Figure 5-4. Location of marinas in the TMDL project area

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5.4. Summary In addition to describing pollution threats, reports prepared by Guam EPA provide an indication of those beaches that may be affected by various source categories. Table 5-4 summarizes pollution threats identified in the §305(b) report for the TMDL project area beaches (Table 5-5 defines the pollution threat codes). Table 5-4 provides a transition into the linkage analysis, where the water quality data are evaluated in a way that considers potential sources. These sources are explored in more detail in the Individual Beach Assessments (Section 8).

Table 5-4. Pollution threats for the TMDL project area beaches Pollution Threats* Water

Fonte

Piti/Asan

Apra

Agat

Beach Beach at Fonte River, West Hagåtña Bay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Port Authority Beach Outhouse Beach Family Beach Togcha Beach aka Agat Beach

Taelayag Umatac Toguan

Beach South of Finile River Nimitz Beach Head of Umatac Bay Toguan Bay

Geus

Merizo Public Pier Park

Site

Name

Wastewater +

S1 , S4

S1, S4

N-21

Adelup Beach Park

W1 , W2, W3

N-22

Adelup Point Beach (West of Adelup Park)

W1 , W2, W3

N-14

Asan Bay Beach

N-15 N-16

Piti Bay Santos Memorial Park Beach

W2 , W3

W1, W2 , W3 W1, W2

United Seamen's Service

N-20 N-18 N-19 S-02 S-03

Port Authority Beach Outhouse Beach Family Beach Togcha Beach - Namo Togcha Beach - Agat Bay Togcha Beach - Beach at SCA

W1, W2 , W5 W1

Bangi Beach

W1 , W2, W3

S-04 S-05 S-06 S-07 S-08

Nimitz Beach Umatac Bay Toguan Bay Merizo Pier - Mamaon Channel Inarajan Pool Inarajan Bay Talofofo Bay First Beach - Talofofo

R3, O8

O7, O8 R3, O4

W1 , W2, W3 + + W2 , W3 +

W1 , W2

S1 , S4 S1 +

S1 + S1 S1

O4 + R3 , O4 R3, 04 O8

W1, W3 + + W1 , W2 + W4, W3

S1 S1

W2, W3

Recreation & Other

S1, S4

N-17

S-17

Stormwater

R1, R2, O8 O8 O8 R3

+ +

Inarajan Pools S-09 W1 , W3 S1 R3 + + + Beach at Inarajan Bay S-10 W1 , W2 , W3 S1 R3 , O6, O8 Head of Talofofo Bay S-11 W1, W3 O6, O8 Talofofo + + First Beach S-18 W1 S1 Ypan Beach Park + Beach (Ipan Public S-12 Ipan Beach W1 R3 Beach) Togcha Beach north of Togcha R5, O6, O8, + S-13 Togcha Bay - Talofofo W3, W4 S1 River O9 + YLIG Tagachan Beach Park S-14 Tagachang Beach W1 R3 + + Pago Beach at Pago Bay S-15 Pago Bay W1, W4 S1 O5, O8 *See Table 5-5for Pollution Threat definitions + Pollution threats were not identified in the specific sources GIS file provided by Guam EPA; however, they were identified through TMDL source assessment. Inarajan

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Table 5-5. Pollution threat code definitions Category

Wastewater

Stormwater

Recreation & Other

Code

Definition

Septic Systems

Sewer line Blockage / Break

SSO

POTW

Industrial point source (GPA effluent)

Stormwater Runoff

Stormwater Runoff (permitted)

Highway / Road / Bridge Runoff

Highway Maintenance and Runoff

Construction

Marina and Recreational Boating

Boat Discharge

Recreational & Tourism Activities

Recreational & Tourism Activities (RUMP)

Golf Course

Debris & Bottom Deposits

Contaminated Sediments

Spill (Oil Underground)

Atmospheric Deposition

Squatters

Wildlife

Historical Confined Animal Feedlot (Chicken)

River Discharge

Nutrient Loading

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6. Technical Approach and LinkageAnalysis Developing TMDLs requires a combination of technical analysis, practical understanding of important watershed processes, and interpretation of watershed loadings and receiving water responses to those loadings. In identifying the technical approach for development of these bacteria TMDLs, the following core set of principles was identified and applied: §

The TMDLs must be based on scientific analysis and reasonable and acceptable assumptions. All major assumptions have been made based on available data and in consultation with appropriate agency staff.

§

The TMDLs must use the best available data. All available data in the watershed were reviewed and were used in the analysis where possible or appropriate.

§

Methods should be clear and as simple as possible to facilitate explanation to stakeholders. All methods and major assumptions used in the analysis are described. The TMDL document has been presented in a format accessible by a wide range of audiences, including the public and interested stakeholders.

An essential component of TMDL development is establishing a relationship between numeric indicators intended to measure attainment of beneficial uses and source loads. The linkage analysis examines connections between water quality targets, available data, and potential sources. Several technical options for the linkage analysis were considered during TMDL development. These options are briefly discussed below (Section 6.1) along with the selected option and application of that option (Section 6.2).

6.1. Options Considered The loading capacity of the TMDL beaches for enterococci is the amount that can be assimilated in the listed segments without exceeding the water quality criteria. Based on USEPA protocols for TMDL development, as well as bacteria TMDLs established in other states and territories, several options were identified. These include: 1. 2. 3. 4. 5.

Load-based approach (mass per unit time) Concentration-based method Reference method with exceedance day frequencies Tidal prism method Concentration-based duration curve approach

The following factors were considered in reviewing each option and selecting a method for determining the loading capacity and allocation method: ü ü ü ü ü ü

Ability of the method to adequately assess the loading capacity Availability of adequate data to apply to the method Ability of the method to account for seasonal variation Degree of uncertainty associated with the method Ease of determining compliance Equity of the methodology

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Twenty Five Guam Beaches

6.1.1. Load-Based Approach (mass per unit time) A load-based approach is defined in terms of a mass per unit time. For bacteria TMDLs, the most common expression of loading capacity using this approach is counts per day. Determination of a loadbased approach requires an estimate of the volume of water or the amount of flow available to assimilate the pollutant load. For a pollutant in a typical river or stream, where flow is only in one direction, the loading capacity, or allowable loading over a given time interval, is determined by calculating the product of flow rate, the water quality criterion concentration (e.g., 35 counts per 100 mL), and a unit conversion factor. For hydrological complex waters, such as coastal beaches, several challenges exist relative to the loadbased approach. First, there is a high degree of uncertainty in estimating loads associated with determining the appropriate receiving water volumes at each beach location. In addition, flow is in more than one direction due to effects of tides, which also adds to the uncertainty in identifying a loading capacity for each listed segment. Finally, determining compliance with these TMDLs would not be a simple task because of the amount of information needed to determine loads associated with each sample event.

6.1.2. Concentration-Based Method Another common approach used for development of bacteria TMDLs is the concentration-based method. Basically, the loading capacity is defined in terms of maximum allowable concentrations. For the impaired beaches, TMDLs using this method would be based on simply attaining the enterococcus concentrations defined in Guamâ&#x20AC;&#x2122;s water quality standards. In other words, enterococcus concentrations must not exceed Guamâ&#x20AC;&#x2122;s water quality criteria in order to meet the TMDLs. This approach addresses most of the factors being considered. Because the loading capacity is equivalent to the numeric criteria, evaluating compliance with the TMDLs is straightforward. There are also adequate data to apply the method. The only uncertainties are those associated with the monitoring program itself. Although seasonal variation is accounted for implicitly, a concentration-based approach adds only limited value to relating TMDL targets to those conditions of greatest concern (e.g., wetweather versus dry-weather). For this reason, it is often difficult to connect concentration-based TMDLs with implementation programs needed to solve water quality problems.

6.1.3. Reference Method with Exceedance Day Frequencies The State of California has utilized an exceedance day frequency to identify loading capacity targets for several beach TMDLs. The focus of this approach recognizes that under certain conditions, natural background loads exert a major effect on water quality criteria violations. Numeric targets are expressed as allowable exceedance days of the single sample criteria. Allowable exceedance days are based on an analysis of conditions at a reference site. Advantages of the method include ease of determining compliance. The approach used in California also accounts for seasonal variation by identifying different summer and winter targets. The approach basically allows for exceptions under which the single sample criteria may be exceeded. Data from reference beaches are needed that describe situations where natural conditions are the only sources. In the case of the TMDL beaches, each site included in these TMDLs is affected by some potential anthropogenic source. Furthermore, the method does not account for the 30-day geometric mean component of the water quality standards. A separate analysis is needed to demonstrate that the geometric mean criteria will also be achieved using an exceedance day frequency approach.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

6.1.4. Tidal Prism Method The tidal prism approach was used to develop TMDLs for recreational beaches in the U.S. Virgin Islands. The concept behind the tidal prism method centers on that amount of water moved in and out of an impaired segment between ebb and flood tides. This provides an estimate of volume per unit time, which enables a loading calculation. The method then uses load estimates from land-based sources to develop components of the TMDLs (e.g., loading capacities and allocations). In short, the tidal prism method estimates the volume of the segment, and then adjusts for tidal flushing, freshwater inflow, and bacteria loads to the waterbody. The major advantage of this method is that targets are expressed as loads; consistent with the strict statutory definition of a TMDL. However, disadvantages are quite similar to those associated with a loadbased approach. Most notably, the need for additional data, uncertainties associated with developing load estimates, and difficulties related to determining compliance.

6.1.5. Concentration-Based Duration Curve Method This approach is a variation of the concentration-based method. Again, the loading capacity is defined in terms of attaining the maximum allowable enterococcus concentrations simply defined in Guamâ&#x20AC;&#x2122;s water quality standards. In addition, TMDL targets are expressed in terms of flow conditions using either stream gage data or flow model estimates (as described earlier in the data analysis section). These flow estimates can be used to identify whether elevated bacteria levels occur during rainfall events (and are likely watershed-driven) or during dry conditions. The advantage of this approach is that both seasonal and flow variations are explicitly considered. This addresses one of the disadvantages of the plain concentration-based approach (i.e., conditions of concern are explicitly identified). There is no uncertainty in the calculation of loading capacities (again, simply the water quality criteria concentrations).

6.2. Concentration-Based Duration Curve Linkage Analysis The approach used to develop these TMDLs is the concentration-based duration curve method. The framework provides a way to assess the loading capacity because it is derived directly from Guamâ&#x20AC;&#x2122;s water quality criteria. In addition, the method takes full advantage of Guamâ&#x20AC;&#x2122;s RBMP information, using the data to examine patterns associated with flow conditions. The approach also accounts for seasonal variation and determining compliance with the TMDLs is relatively straightforward. There is equity in the method in that all sources are expected to meet the concentration-based targets. Finally, the concentration-based duration curve method supports a meaningful transition into implementation programs. Because water quality data are used to examine flow-related patterns, monitoring information can be used to determine source areas and delivery mechanisms associated with these different conditions. This, in turn, can be used to identify those actions most likely needed to address water quality problems. The remainder of this section discusses general application of the concentration-based duration curve framework, building off of the data analyses presented in Section 4. Detailed discussions for each beach, including linking sources to the water quality data and numeric targets, are presented in Section 8.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

6.2.1. Pattern Analysis The 25 beaches that are the focus of this TMDL report represent an array of situations, as evidenced by information presented in the data summary and source assessment. One way to capitalize on the wealth of ambient beach monitoring information is to examine patterns associated with potential source area and delivery mechanisms. The duration curve method is one option for building a framework that supports pattern analysis and the subsequent linkage of data analysis to potential sources. This method provides the opportunity to connect water quality data with TMDLs and subsequent implementation efforts through pattern analysis. To take advantage of this approach, all duration curves developed for the TMDLs were created using comprehensive flow data from USGS flow gages. Gaps in the flow record were addressed using a rainfall-runoff model to create a comprehensive hydrology dataset (Section 4.4.2). Patterns in geometric means and variability of flow regimes identify the flow conditions under which exceedances or elevated levels are occurring. Identifying these conditions is useful in connecting observed bacteria levels to potential sources. Specifically, the duration curve framework allows for trends and patterns to be determined across different flow regimes using geometric means and 90th percentiles. These values enable a comparison of patterns between flow regimes, seasons, and across the beach monitoring sites. In addition to being a criteria value for enterococci in Guamâ&#x20AC;&#x2122;s water quality standards, the geometric mean provides a measure of central tendency; an important factor to guide long-term program implementation efforts. The 90th percentile, on the other hand, complements the geometric mean by providing a measure that reflects recurring shorter-term problems (e.g., sewer line breaks or spills). These geometric and 90th percentile values for all of the beaches are presented in the following sections. Spatial patterns are examined in Section 6.2.1.1, and seasonal patterns are discussed in Section 6.2.1.2. 6.2.1.1. Spatial Patterns Using the geometric and 90th percentile measures, the next step in the linkage analysis is to examine spatial patterns at all 25 TMDL beach sites. Table 6-1 summarizes the geometric means associated with each duration curve zone for the RBMP monitoring sites in the project area. Table 6-2 provides a summary of the 90th percentiles for the same sites. This information was developed using all data regardless of season. Section 4.5 above presents example data analyses for flow- and concentration-based duration curves. These analyses were applied to available data for each beach and the geometric means and 90th percentile enterococci concentrations for each flow regime were calculated and are presented in the tables below. Table 6-1 enables a comparison of patterns between duration curve zones by site. It also highlights sites and duration curve zones that exceed Guamâ&#x20AC;&#x2122;s geometric mean criteria (those cells are shaded). Similarly, Table 6-2highlights sites and duration curve zones where the 90th percentile exceeds Guamâ&#x20AC;&#x2122;s instantaneous maximum criteria. Examining the geometric mean on a year-round basis, the greatest concentrations for each site occur under high flow conditions (Table 6-1). This analysis identifies the areas and conditions where bacteria sources have the most long-term, chronic effect. Geometric means are particularly high at the head of Talofofo Bay (S-11) on the eastern side of the island. Stormwater discharges in this drainage should be a focus of implementation efforts. The 90th percentile results show more expansive exceedances (Table 6-2). Specifically, all beaches on the southern end of Guam have exceedances of the high flow conditions and nearly all of them also have exceedances of during moist conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-1. TMDL beach data summary (Geometric Mean – year round) Water Fonte

Piti/Asan

Apra

Beach Beach at Fonte River, West Hagåtña Bay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Outhouse Beach Family Beach Port Authority Beach Togcha Beach aka Agat Beach

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Beach South of Finile River Nimitz Beach Head of Umatac Bay Toguan Bay Merizo Public Pier Park Inarajan Pools Beach at Inarajan Bay Head of Talofofo Bay First Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park Beach at Pago Bay

Site ID

High

Duration Curve Zone Moist Mid Dry

Low

N-21

123

N-22

N-14

207

N-15 N-16

77 203

26 70

23 38

15 24

15 26

N-17

N-18 N-19 N-20 S-02 S-03 S-17

15 11 24 150 223 191

14 11 16 36 32 33

13 12 13 23 25 28

11 10 11 19 17 31

11 10 19 51 42 54

S-04

1304

136

S-05 S-06 S-07

203 534 734

40 53 204

28 27 71

27 18 51

51 17 39

333 206 1,203 2,052 41

79 42 130 418 15

43 20 49 123 12

41 19 29 37 11

47 18 27 40 9

191 14 121

27 14 25

16 15 20

15 13 16

14 13 29

S-08 S-09 S-10 S-11 S-18 S-12 S-13 S-14 S-15

Shaded cells indicate those zones where the geometric mean criterion was exceeded. This is indicative of potential long-term, chronic problems under those conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-2. TMDL beach data summary (90th percentile – year round) Water Fonte

Piti/Asan

Apra

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Site ID

High

Duration Curve Zone Moist Mid Dry

Low

N-21

941

203

110

N-22

276

N-14

2,357

340

241

124

202

N-15 N-16

1,016 2,088

145 629

118 305

52 167

64 206

N-17

N-20 N-18 N-19 S-02 S-03 S-17

42 24 117 3,375 9,006 11,564

47 10 75 312 281 301

31 31 41 131 254 221

10 10 20 74 98 203

20 10 104 429 290 218

S-04

21,162

2,501

470

259

1,111

S-05 S-06 S-07

7,415 11,199 12,914

281 676 4,106

148 238 424

218 120 433

263 73 211

2,475 7,114 14,694 9,896 671

627 565 1,467 3,451 80

457 80 237 731 23

264 85 237 227 10

189 54 111 253 9

162

14,694 51 1,686

387 59 236

52 53 97

52 30 63

32 20 256

S-08 S-09 S-10 S-11 S-18 S-12 S-13 S-14 S-15

Shaded cells indicate those zones where the instantaneous criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

6.2.1.2. Seasonal Patterns Developing duration curve intervals based on complete flow datasets enables a closer look at factors, such as seasonality. This provides the opportunity to examine patterns that may be associated with other potential bacteria sources. For example, bacteria delivered through seeps connected to stormwater ponds are more likely to affect beach monitoring data during the wet season. In contrast, bacteria contributed from more continuous sources (e.g., leaky sewer lines or failing septic systems) will exert a greater effect during the dry season. As illustrated previously in Section 6.2.1.1, high flow conditions are runoff dominated flow conditions that are influenced by storm events. Therefore, it is typical to see elevated wet season trends under high

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

flow or moist flow conditions. Dry season exceedances occurring under these runoff dominated flow conditions also occur and are associated with the long periods of no rain that allow for the build-up of pollutants (bacteria bound particles among others) to be washed-off during these sparse rain events. In contrast, elevated bacteria levels under low flow conditions and in dry season samples may be indicative of dry weather sources that are on-going such as leaky sewer lines, seeping septic systems, or untreated sewage discharge. Consistently high dry season geomeans or those comparably high to wet season geomeans across all flow regimes may also strongly suggest the influence of dry weather point sources. Seasonal analyses for Togcha Bay (S-13) are presented as an example. As illustrated in Figure 6-1, the effect of stormwater runoff and intermittent dry weather sources on bacteria concentrations is evident at Togcha Bay. As shown, elevated wet-season geomeans in the high flow regime (as well as high maximum values, representing more sporadic events, across all regimes except low) suggests stormwater issues or short-term issues such as SSOs, seeps connected to stormwater ponds/sources, and stormwater ponds overflowing. On the other hand, the intermittently elevated dry season geomeans and maximum values across all flow regimes is indicative of sporadic loading from continuous and/or point sources that affect the waters regardless of season or flow condition. Overall, elevated bacteria levels at Togcha Bay are particularly a concern during wet season, highflow conditions.

Figure 6-1. Wet versus dry season comparison for Togcha Bay Similar to the analysis of spatial patterns, the geometric mean and 90th percentile serve as the primary measures for examining seasonality across all RBMP sites. Geometric means of all sites during the dry and wet seasons are presented in Table 6-3and Table 6-4, respectively. The 90th percentile values of all sites during the dry and wet seasons are presented in Table 6-5and Table 6-6, respectively. For the 90th percentile analyses, the wet weather concentrations are typically higher than during dry-weather (although there are notable exceptions, which are described in the Individual Beach Assessments [Section 8]). There is less of a pattern for the geometric mean analyses, indicating that there are multiple sources of bacteria affecting the beaches differently; thereby, supporting the need for the detailed beach analyses presented below in Section 8.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-3. TMDL beach data summary (Geometric Mean – dry season) Water Fonte

Piti/Asan

Apra

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Site ID N-21 N-22 N-14 N-15 N-16

High

Duration Curve Zone Moist Mid Dry

Low

124

236 226 404

66 39 66

36 22 31

23 15 23

26 14 26

33 30 9 33 115 122 219

14 17 12 16 29 27 26

10 12 11 12 22 26 31

11 11 11 11 16 16 32

14 11 10 17 25 27 48

726 145 946 5,526

91 37 71 302

49 30 26 51

32 26 17 49

50 28 17 39

990 37 516 3,102 36

82 58 116 388 18

35 20 48 103 13

38 18 28 36 10

47 18 27 40 9

38 16 289

17 14 18

14 12 17

14 12 15

14 12 24

N-17 N-20 N-18 N-19 S-02 S-03 S-17 S-04 S-05 S-06 S-07 S-08 S-09 S-10 S-11 S-18 S-12 S-13 S-14 S-15

Shaded cells indicate those zones where the geometric mean criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-4. TMDL beach data summary (Geometric Mean – wet season) Water Fonte

Piti/Asan

Apra

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Site ID N-21 N-22 N-14 N-15 N-16

High

Duration Curve Zone Moist Mid Dry

Low

123

206 73 196

53 23 72

42 24 48

19 13 32

50 28 33

13 15 12 24 156 244 187

13 13 10 17 41 34 37

14 15 13 15 26 23 24

11 9 9 14 36 24 30

9 14 11 45 139 78 64

1426 213 518 656

165 41 50 188

85 24 28 98

56 34 34 79

224 117 ----

313 227 1,260 1,990 41

79 39 133 425 14

52 20 50 164 11

70 22 37 68 13

215 14 116

31 14 28

20 20 23

25 13 19

N-17 N-20 N-18 N-19 S-02 S-03 S-17 S-04 S-05 S-06 S-07 S-08 S-09 S-10 S-11 S-18

------

S-12 S-13 S-14 S-15

-32 135

Shaded cells indicate those zones where the geometric mean criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions. Cells flagged with “—“ have no data available for that flow duration zone

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-5. TMDL beach data summary (90th percentile – dry season) Water Fonte

Piti/Asan

Apra

Beach Beach at Fonte River, West Hagåtña Bay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay Beach at Piti Bay (Tepungan Beach) United Seamen’s Service Beach (USO Beach) Port Authority Beach Outhouse Beach Family Beach Togcha Beach aka Agat Beach

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Site ID N-21 N-22 N-14 N-15 N-16

High

Duration Curve Zone Moist Mid Dry

Low

527

278

106

264

569 565 1,903

493 352 569

240 120 196

128 52 158

160 31 179

540 605 9 136 4,312 6,362 18,703

81 168 10 35 248 152 163

10 30 10 39 122 260 213

20 10 10 20 63 83 243

43 20 10 99 108 63 160

9,527 1,647 8,571 17,385

953 206 1,377 9,466

625 149 236 361

196 218 98 393

933 120 73 211

3,793 75 8,405 9,614 40

1,764 1,042 824 5,081 123

426 85 148 408 31

246 85 213 178 10

189 54 111 253 9

135

60 28 3,459

46 67 65

36 20 51

41 34 45

32 20 128

N-17 N-20 N-18 N-19 S-02 S-03 S-17 S-04 S-05 S-06 S-07 S-08 S-09 S-10 S-11 S-18 S-12 S-13 S-14 S-15

Shaded cells indicate those zones where the instantaneous criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 6-6. TMDL beach data summary (90th percentile – wet season) Water Fonte

Piti/Asan

Apra

Agat

Taelayag Umatac Toguan Geus Inarajan Talofofo

Togcha YLIG Pago Note:

Site ID N-21 N-22 N-14 N-15 N-16

High

Duration Curve Zone Moist Mid Dry

Low

951

201

115

144

271

2,503 1,020 2,015

338 104 650

196 111 483

63 50 172

333 186 180

49 31 28 102 3,335 8,892 9,936

41 36 10 80 354 374 532

67 43 33 45 130 233 214

20 10 10 38 245 136 128

10 47 22 313 1,974 296 229

24,192 10,903 11,200 12,080

2909 301 549 3,297

458 143 237 431

536 197 370 695

1,888 463 ----

2,064 8,787 15,113 9,804 697

588 484 1,738 3,441 61

453 74 287 857 18

581 92 249 310 48

143

15,251 52 1,571

439 41 279

166 90 143

68 27 102

N-17 N-20 N-18 N-19 S-02 S-03 S-17 S-04 S-05 S-06 S-07 S-08 S-09 S-10 S-11 S-18

------

S-12 S-13 S-14 S-15

-452 2,793

Shaded cells indicate those zones where the instantaneous criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions. Cells flagged with “—“ have no data available for that flow duration zone

6.2.2. Relationship to Other Indicators The use of other water quality parameters as indicators of bacteria is a valuable means of conserving and utilizing monitoring resources if a relationship can be established. Given limited turbidity data, a thorough and sound linkage between bacteria and turbidity cannot be made for the 25 TMDL beaches in Guam. A general assessment of the turbidity data, however, can be presented to draw conclusions on the general quality of some beaches.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

The available turbidity data include observations for 14 Guam beaches from 2011 through half of 2012. Each beach has between one and six turbidity observations. The sites for which turbidity samples were taken are listed in Table 6-7. These tables have also been classified by waterbody type (beach or bay) for further categorization. Turbidity samples at beach sites ranged from 0.15 to 4.3 NTU; whereas, bay sites ranged from 0.1 to 65.9 NTU. As shown in Table 6-7, average turbidity concentrations were highest at Umatac Bay, Inarajan Bay, and Talofofo Bay. A temporal distribution of turbidity samples is presented in Figure 6-2 with bay sites and beach sites distinguished. This illustration confirms that bay sites generally had higher turbidity concentrations than beach sites for most sample days.

Table 6-7. Summary of available turbidity data Turbidity Site ID

RBMP Site

Site Name

Waterbody Type

Average (NTU)

AGMFb

N-21

Adelup Beach Park

Bay

3.30

ASM22

N-22

Adelup Point Beach

Bay

1.70

ASM14

N-14

Asan Bay Beach

Bay

0.97

PBM15

N-15

Piti Bay

Bay

2.11

PBM16

N-16

Santos Memorial Park

Beach

0.85

APM18

N-18

Outhouse Beach

Beach

1.00

APMOb

N-19

Family Beach

Beach

1.11

ATMN

S-02

Togcha Beach - Namo R.

Beach

2.31

ULMUEb

S-06

Umatac Bay

Bay

14.20

INBM10

S-10

Inarajan Bay

Bay

5.76

TUM11

S-11

Talofofo Bay

Bay

6.80

TBM18

S-18

First Beach

Beach

0.95

TGAM14

S-14

Tagachang Beach

Beach

0.66

PGM15

S-15

Pago Bay

Bay

0.15

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 6-2. Distribution of available turbidity data Guam bays such as Umatac Bay, Inarajan Bay, and Talofofo Bay also demonstrate high bacteria concentrations throughout the year. Whether these bacteria concentrations are related to increased turbidity or whether turbidity can be used as a surrogate for bacteria warrants further investigation. To establish a sound relationship between bacteria and turbidity, it is recommended that turbidity and bacteria monitoring occur on the same day. Further, turbidity is also a good indicator of stormwater runoff or suspended material associated with wind action. Measuring ambient levels of turbidity can be useful in identifying turbidity trends with respect to runoff or wind events, thereby establishing a deeper relationship with bacteria and flow conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

7. TMDL Development These TMDLs are designed to address bacteria impairments on 25 water quality-limited segments located in the GuamTMDL project area. Section 303(d)(1)(C) of the Federal Clean Water Act requires that TMDLs must be “… established at a level necessary to implement the applicable water quality standards with seasonal variations and a margin of safety which takes into account any lack of knowledge concerning the relationship between effluent limitations and water quality”. Federal regulations provide further definition regarding the structure and content of Total Maximum Daily Loads. TMDLs are defined as the sum of the individual waste load allocations (WLAs), load allocations (LAs), and the margin of safety. TMDLs can be expressed in terms of “… mass per time, toxicity, or other appropriate measure” [40 CFR §130.2(i)]. WLAs are the portion of the receiving water’s loading capacity allocated to existing or future point sources [40 CFR §130.2(h)]. LAs are the portion of the receiving water’s loading capacity allocated to existing or future nonpoint sources or to natural background sources [40 CFR §130.2(g)]. Conceptually, this definition is denoted by the equation TMDL = Σ WLAs + Σ LAs + MOS Under the current regulatory framework for development of TMDLs, calculation of the loading capacity for impaired segments identified on the §303(d) list is an important step. EPA’s regulation defines loading capacity as “the greatest amount of loading that a water can receive without violating water quality standards”. The loading capacity provides a reference, which helps guide pollutant reduction efforts needed to bring a water into compliance with standards.

7.1. Establishment of the TMDL The linkage analysis provides the quantitative basis for determining the loading capacities for enterococcifor the impaired beaches. Because TMDL calculations are based on beneficial uses and associated numeric standards, attainment of the TMDL numeric targets will result in attainment of water quality standards. As described in Section 6.2, a concentration-based duration curve framework was applied to assess the loading capacity. This is derived directly from Guam’s water quality criteria and also evaluates the data to examine patterns associated with flow conditions. It accounts for seasonal variation through the analyses of different flow regimes and wet- or dry-weather conditions. This linkage analysis also provides information to support meaningful implementation programs as the analyses identify source areas and transport mechanisms impacting beach water quality.

7.2. Loading Capacity and Allocations Table 7-1presents an example TMDL for all of the M-2 beach locations, while Table 7-2 presents the TMDL for M-3 beach locations (Table 1-1 presents the marine water category for each impaired beach). These tables identify the loading capacity and allocations. WLAs apply to point sources, including the permitted treatment plants (Table 5-2) and LAs apply to nonpoint sources. These concentration-based values apply across all flow zones. Section 8 presents TMDLs for each beach, including a comparison with the existing pollutant concentrations by flow regime. If the existing pollutant loading from the point and nonpoint sources exceeds allocations, reductions required were calculated to meet the TMDL, and thus water quality standards.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 7-1. TMDLs and Allocations for M-2 Beaches TMDL Component

Enterococci Concentration (# / 100 mL) Geometric Mean

TMDL

Future Growth

Waste Load Allocation

Load Allocation

35 Instantaneous Maximum

TMDL

104

Future Growth

104

Waste Load Allocation

104

Load Allocation

104

Table 7-2. TMDLs and Allocations for M-3 Beaches TMDL Component

Enterococci Concentration (# / 100 mL) Geometric Mean

TMDL

Future Growth

Waste Load Allocation

Load Allocation

35 Instantaneous Maximum

TMDL

276

Future Growth

276

Waste Load Allocation

276

Load Allocation

276

7.3. Margin of Safety The Clean Water Act requires that each TMDL be established with a margin of safety. The statutory requirement that TMDLs incorporate a margin of safety is intended to account for any uncertainty or lack of knowledge concerning the relationship between pollutant loading and water quality. The MOS also accounts for uncertainty in available data or in the actual effect controls will have on loading reductions and receiving water quality. A margin of safety is expressed as unallocated assimilative capacity or conservative analytical assumptions used in establishing the TMDLs (e.g., derivation of numeric targets, modeling assumptions

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

or effectiveness of proposed management actions). The margin of safety may be implicit, as in conservative assumptions used in calculating the loading capacity, WLAs, and LAs. The margin of safety may also be explicitly stated as an added, separate quantity in the TMDL calculation. The MOS may also be a combination of both. These TMDLs use an implicit MOS, through inclusion of two conservative assumptions. First, the TMDLs do not account for mixing in the receiving waters and assumes that zero dilution is available. Realistically, influent water will mix with the receiving water and become diluted below the water quality standard, provided that the receiving water concentration does not exceed the TMDL concentration. Second, the goal of attaining standards at the point of discharge does not account for losses due to die-off and settling of indicator bacteria that are known to occur. In addition, the concentration criteria accounts for seasonal variations and critical conditions.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

8. Individual Beach Assessments and TMDLs An important part of the transition from TMDL targets to program implementation is information derived from site-specific analyses. In particular, an in-depth evaluation of monitoring data relative to potential local sources that may affect water quality at each station adds value to the overall process. Individual beach assessments can be used to guide development of strategies that address documented problems. The purpose of this section is to present a beach-by-beach analysis and the TMDL for each location. Connections between observed water quality patterns, factors that affect each site, and potential solutions are highlighted. Individual assessments provide brief background material on each beach including watershed settings and potential sources local to each beach. Water quality data from 2001 through 2011 are examined for patterns and trends that may be indicative of certain potential sources or conditions specific to that area. Table 8-1 summarizes the list of GIS coverages that were considered in developing individual beach assessments.

Table 8-1. GIS data layers considered in individual beach assessments Data Category

Description

Coast

Guam coast line

Contours

Elevation contours (10 meter intervals) used to characterize topography

Beach TMDL Sites

Location of Recreational Beach Monitoring Program stations

WWTP

GWA Waste Water Treatment Plant locations

Marinas

Location of Guam marinas under jurisdiction of Port Authority of Guam

Streets

Streets mapped in Guam EPA data base as of October 2008

Buildings

Buildings identified in Guam EPA data base as of June 2006

Sewered Buildings

Buildings in data base identified as connected to sewer

Non-sewered Buildings

Buildings in data base identified as not connected to sewer

Main Sewer

Main sewer lines under jurisdiction of GWA

Lateral Sewer

Lateral sewer lines identified by GWA

Pump Station

Location of GWA sewer pump / lift stations

Fittings

Location of GWA sewer fittings

Manhole

Sewer manholes

SIA Ponding Basins

Surface Impoundment Areas identified by Guam Dept. of Public Works

Geology

Limestone

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8.1. Adelup Beach Park (N-21) Adelup Beach Park (RBMP site N-21) is in the northern Guam watershed and is west of the village of HagĂĽtĂąa. It lies along the shore of Agana Bay and is east of Adelup Point. Fonte River discharges into Agana Bay and is located east of the Adelup Beach Park. Figure 8-1shows the location of Adelup Beach Park and an aerial view of the area.

Figure 8-1. Location of Adelup Beach Park relative to other TMDL sites Data collected weekly at the Adelup Beach Park site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-2, 37 percent of beach days at Adelup Beach Park had a beach advisory, based on data provided since 2001. Although thisbeach advisory frequency may be modest, it is nearly twice as much as Adelup Point Beach (RMBP site N-22) which is west of Adelup Beach Park and separated by Adelup Point.

Bacteria Total Maximum Daily Loads

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Figure 8-2. Beach advisory frequency at Adelup Beach Park The range of bacteria at Adelup Beach Park from 2001 through 2011 is presented in Figure 8-3 as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous water quality standards and, to a lesser extent, geomean water quality standards nearly every year. The geometric mean of all individual samples was 26 counts /100 mL, while the 75th and 90th percentiles were 52 and 219 counts /100 mL, respectively.The rolling five-week geomean ranges from 9 to 532 counts/100 mL (Figure 8-3).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-3. Enterococci data analysis at Adelup Beach Park Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Adelup Beach Park is presented in Figure 8-4. The central tendency of bacteria concentrations on a yearly basis falls below the geomean WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS). Annual variability differs year to year with maximum concentrations exceeding the instantaneous WQS every year in the study period. Notably, in recent years beginning in 2009 the 75th percentile concentrations have consistently fallen above 35counts/100mL, approaching the instantaneous WQS (and exceeding it in 2011).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-4. Annual analysis of enterococcus data for Adelup Beach Park Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. Figure 8-5 shows the seasonal variability of bacteria concentrations at Adelup Beach Park. Concentrations,at least an order of magnitude greater than the instantaneous WQS, were consistently observed during the wet season. During the wet-weather months of July through October, 25 percent of samples were above the instantaneous WQS on a monthly basis. Comparatively, exceedances during the dry season demonstrated greater variability as maximum exceedances ranged from 300 to 24,000 counts/100mL.Despite the variability in maximum dry season concentrations observed, water quality standards were not regularly exceeded. In fact, 75 percent of the samples were below the instantaneous WQS on a monthly basis. Overall, wet season sources are likely contributors to the high concentrations observed from July through October at Adelup Beach Park.

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-5. Seasonal variation at Adelup Beach Park Duration Curve Analysis A duration curve framework is used in Figure 8-6, Figure 8-7, and Figure 8-8 to relate bacteria concentrations to hydrologic conditions. These figures confirm that most exceedances occur under high flow conditions. As shown in Figure 8-6, over 75 percent of samples taken during high flow conditions were greater than the instantaneous WQS. As shown in Figure 8-7, most of the exceedances under high and moist flow conditions occur during the wet season or a stormwater runoff event. The few exceedances under dry and low flow conditions may be attributed to infrequent rainfall events that washoff bacteria-bound particles after long periods of dry weather. The elevated dry weather observances, however, may be indicative of wastewater sources in the area such as leaky sewer mains or failing septic systems. Such sources are most evident under dry weather conditions, but can also influence the quality of stormwater runoff. The duration curve analysis indicates that most exceedances are related to wet-weather events, but elevated bacteria levels are also noticeable during the dry season (Figure 8-8).

Bacteria Total Maximum Daily Loads

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Figure 8-6. Water quality duration analysis of Adelup Beach Park

Figure 8-7. Detailed water quality duration analysis of Adelup Beach Park

Bacteria Total Maximum Daily Loads

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Figure 8-8. Wet versus dry seasonal analysis for Adelup Beach Park Potential Sources 5 The Adelup Beach Park drainage areaconsists of a mix of developed and undeveloped land (Figure 8-9). The area immediately surrounding Site N-21 including Adelup Point, the western shoreline, and inland area is high-intensity developed land. Vegetated cover, primarily evergreen forest, is mostly inland and south and southeast of Adelup Beach Park. Zoned land uses in Figure 8-10 confirm a substantial amount of single-family uses, commercial uses, and multiple dwelling uses along the shore and inland near Adelup Beach Park. A significant portion of drainage area is also dedicated to military use which coincides with the high-and open-intensity development shown inland in Figure 8-9. Potential sources of bacteria are demonstrated in Figure 8-9 and Figure 8-10. As shown in Figure 8-9, to the east of Adelup Beach Park, HagĂĽtĂąa STP discharges into Agana Bay and less than five miles upstream Fonte River, an unpermitted point source discharge and an untreated sewage discharge are identified. Other potential sources identified in the area include stormwater runoff and untreated sewage discharge, which may impact bacteria levels at Adelup Beach Park and Adelup Point Beach. Although a dense network of sewer mains is identified in the commercial and residential areas along the shore (Figure 8-10), a significant number of non-sewered buildings are present inland (Figure 8-9). The presence of sewer mains and septic systems can influence bacteria concentrations if maintenance is poor and systems are failing. Other sources identified by Guam EPA that can also influence water quality include historic sewer line breaks and blockages, stormwater runoff from highway sources, and river discharge from upstream sources (Table 8-2). Although many of these sources may be considered as wastewater sources, they can influence the quality of stormwater runoff significantly.

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Figure 8-9. Land cover and location of Adelup Beach Park relative to potential source areas Table 8-2. Beach specific potential source summary (Site N-21: Adelup Beach Park) Site ID

N-21

Source Name (notes)

Type Wastewater

Historic sewer line blockage/break

Stormwater

Highway maintenance and Runoff

Other

River discharge

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Figure 8-10. Location of Adelup Beach Park relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Adelup Beach Park is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed between the wet weather months of July and October (Figure 8-5). Significant exceedances under high flow conditions as well as runoff event exceedances under moist to dry flow conditions confirmwet-weather issues influence water quality (Figure 8-6). Wet-weather sources such as stormwater runoff may occur during both the wet- and dry-seasons; however, a considerable amount of elevated concentrations during the dry weather is evident suggesting the presence of dry-weather sources. These water quality trends suggest that wet-weather and, to a lesser extent, dry-weather sources may be contributing to elevated bacteria levels. These trends are consistent with the presence of potential sources identified including a dense sewer drainage network near the shore of Agana Bay and several nonsewered buildings located inland and upstream of Fonte River.The dense impervious cover near the site and the ability of Fonte River to transport upland sources makes stormwater runoff a viable threat to water quality. The technical analyses presented in this assessment of Adelup Beach Park describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-3 presents the TMDL for Adelup Beach Park, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-3 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-3. TMDL summary (Site N-21: Adelup Beach Park) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

123

Instantaneous

104

941

203

110

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-4 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-4. Reductions required to meet the TMDL (Site N-21: Adelup Beach Park) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

72% 80%

--63%

--2%

-----

72% 89%

--48%

--9%

-----

--28%

Note: --- indicates no reductions required for this condition

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8.2. Adelup Point Beach (West of Adelup Point) (N-22) Adelup Point Beach (West of Adelup Point) (RBMP site N-22) is in the northern Guam watershed and is west of the village of Hagåtña. It lies along the shore of Agana Bay and is west of Adelup Point. It is the most eastern beach between Adelup and Asan Points, also known as “the devil’s horns.” The shore between these two points has historic significance as it was the site where the battle for Guam took place to reclaim Guam from the Japanese in 1944. Figure 8-11shows the location of Adelup Point Beach and an aerial view of the area.

Figure 8-11. Location of Adelup Point Beach relative to other TMDL sites Data collected weekly at the Adelup Point Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-12, based on data provided since 2001, 17 percent of beach days at Adelup Point Beach had a beach advisory. This frequency of beach advisories is low compared to other beach advisory frequencies in the northern Guam watershed.

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Figure 8-12. Beach advisory frequency at Adelup Point Beach The extent of bacteria present at Adelup Point Beach from 2001 through 2011 is presented in Figure 8-13 as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards nearly every year with the exception of2005. The geometric mean of all individual samples was 16 counts /100 mL, while the 75th and 90th percentiles were below the instantaneous WQS at 20 and 63 counts /100 mL, respectively. These low 90th and 75th percentiles indicate that the instantaneous samples were generally below the WQS and exceedances were infrequent maximum concentration observations. The rolling geomean ranged from 9 counts/100 mL to 120 counts/ mL.

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Figure 8-13. Enterococci data analysis at Adelup Point Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Adelup Point Beach is presented in Figure 8-14. As shown, the central tendency of bacteria concentrations on a yearly basis did not exceed the instantaneous WQS and fell below35 counts/100 mLand (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS). Nearly every year except 2005, maximum concentration observations exceeded the instantaneous WQS. Notably, significantly low bacteria concentrations and minimal variability were observed during 2005 through 2007. After 2007, however, bacteria concentrations generally increased as indicated by the spike in 75th percentile concentrations.

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Figure 8-14. Annual analysis of enterococcus data for Adelup Point Beach Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons at Adelup Point Beach. As shown in Figure 8-15, maximum concentrations exceeding the instantaneous WQS were observed nearly every month. The seasonal analysis does not portray any stark trends between the seasons; however, greater variability in bacteria concentrations is evident in the wet season months compared to the dry season months. Overall, there are no significant seasonal trends to suggest a driving force; therefore, contribution of bacteria to Adelup Point Beach is likely from a variety of sources.

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Figure 8-15. Seasonal variation at Adelup Point Beach Duration Curve Analysis A duration curve framework is used in Figure 8-16, Figure 8-17, and Figure 8-18 to relate bacteria concentrations to hydrologic conditions. These figures confirm annual and seasonal analyses that exceedances are generally infrequent as less than 25 percent of samples, separated by flow regime, exceed the instantaneous WQS. The duration curve analysis does illustrate that the highest bacteria concentrations are observed under high flow conditions (Figure 8-16). In further examination, Figure 8-17 demonstrates that exceedances under high and moist flow conditionsoccur during the wet season or a stormwater runoff event. In Figure 8-18, the influence of dry-weather sources can be seen under high and moist flow conditions where dry weather observations either exceeded or equaled wet weather observations. This is expected as long antecedent periods of no rainfall cause the build-up of bacteriabound particles, which are washed-off in a dry season rainfall event. Overall, there are not a significant number of exceedances observed at Adelup Point Beach. The few exceedances, however, mostly occurred under high flow conditions during the wet season or a stormwater runoff event (which can occur during the wet- or dry-season months). Exceedances during the dry season are likely attributed to storm events during the dry season but may also be influenced by local wastewater sources.

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Figure 8-16. Water quality duration analysis of Adelup Point Beach

Figure 8-17. Detailed water quality duration analysis of Adelup Point Beach

Bacteria Total Maximum Daily Loads

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Figure 8-18. Wet versus dry seasonal analysis for Adelup Point Beach Potential Sources 5 The drainage area to Adelup Point Beach consists of mixed land uses. High-intensity development is present in Adelup Point and the surrounding shoreline (Figure 8-19). Immediately inland from Site N-22 is zoned agricultural land that consists of evergreen forest, shrub, and grassland cover (Figure 8-20). Zoned land uses in Figure 8-20confirm a substantial amount of single-family uses, commercial uses, and multiple dwelling uses are present along the shore and inland. A significant portion of land is also dedicated to military use which coincides with the high- and open-intensity development shown inland in Figure 8-19. Potential sources are demonstrated in Figure 8-19and Figure 8-20. As shown in Figure 8-19,to the east of Adelup Point Beach, HagĂĽtĂąa STP discharges into Agana Bay,and an untreated sewage discharge has been identified as a specific potential source within the vicinity of Site N-22. Although Fonte River drains to the west of Adelup Point, potential sources identified along nearby river reaches include stormwater runoff, unpermitted point source discharge, and untreated sewage discharge. In the upper portions of the watershed, a number of non-sewered buildings present an extensive network of septic systems that may contribute to water quality impairment downstream. Other sources identified by Guam EPA that may influence water quality include sewer line breaks and blockages, stormwater runoff from impervious surfaces and roadway infrastructures (Table 8-5).

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Figure 8-19. Land cover and location of Adelup Point Beach relative to potential source areas Table 8-5. Beach specific potential source summary (Site N-22: Adelup Point Beach) Site ID

Wastewater N-22

Source Name (notes)

Type

Stormwater

Sewer line block/break Stormwater runoff Highway maintenance and Runoff

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-20. Location of Adelup Point Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Adelup Point Beach is demonstrated through an analysis of water quality monitoring data at this site. Although no seasonal trends stand out, water quality duration curves illustrate that elevated bacteria concentrations occur under all flow regimes and during both wet and dry seasons. These trends indicate that there is no significant driving source of bacteria but a combination of dry-weather and wet-weather sources affecting the water quality at Adelup Point Beach. The high intensity developed cover near the shore, as well as the septic systems and sewer line networks located upstream are contributing factors to stormwater runoff. Wastewater sources such as untreated sewage discharges may also directly affect the water quality at Adelup Point Beach. The technical analyses presented in this assessment of Adelup Point Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-6 presents the TMDL for Adelup Point Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-6 also shows the observed concentrations

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Twenty Five Guam Beaches

associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-6. TMDL summary (Site N-22: Adelup Point Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

276

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-7 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-7. Reductions required to meet the TMDL (Site N-21: Adelup Point Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

53% 61%

-----

--62%

-----

Note: --- indicates no reductions required for this condition

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

8.3. Asan Bay Beach (N-14) Asan Bay Beach (RBMP site N-14) is in the northern Guam watershed. The site is located in between Adelup and Asan Points, also known as “the devil’s horns.” Asan Bay Beach has historic significance as it was the site where the battle for Guam took place to reclaim Guam from the Japanese in 1944. Figure 8-21 shows the location of Asan Bay Beach and an aerial view of the area.

Figure 8-21. Location of Asan Bay Beach relative to other TMDL sites Data collected weekly at the Asan Bay Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-22, based on data provided since 2001, 52 percent of beach days at Asan Bay Beach had a beach advisory. This frequency of beach advisories is a significant public health issue and is also a concern for several northern beaches including Piti Bay where the beach advisory frequency reaches 90 percent.

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Figure 8-22. Beach advisory frequency at Asan Bay Beach The extent of bacteria present at Asan Bay Beach from 2001 through 2011 is demonstrated in Figure 8-23 as instantaneous and five-week geomean samples of enterococci data. As shown, there is high variability among the samples with instantaneous and geomean water quality standards exceedances occurring every year. The geometric mean of all individual samples was 46 counts /100 mL, while the 75th and 90th percentiles were 122 and 402 counts /100 mL, respectively.The rolling five-week geomean ranges from 9 to 706 counts/100 mL (Figure 8-23).

Bacteria Total Maximum Daily Loads

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Figure 8-23. Enterococci data analysis at Asan Bay Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Asan Bay Beach illustrates that maximum observed concentrations exceeded the instantaneous WQS every year(Figure 8-24).In addition, significant variability in bacteria concentration is evident. In most years, the 75th percentile exceeded the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS).

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-24. Annual analysis of enterococcus data for Asan Bay Beach Seasonal Analysis A seasonal analysis of bacteria data for Asan Bay Beach from 2001 to 2011 is presented in Figure 8-25. As shown, maximum observed concentrations were observed on a monthly basis during both the dry and wet seasons. Althoughmonthly medians were greater during the wet season than the dry season, dry season monthly samples showed significant variability with 75th percentile concentrations nearing the instantaneous WQS. In sum, while the wet season results do tend to be higher, the seasonal analysis does not display any significant differences between the two seasons. This strongly suggests that bacteria sources are present throughout the year.

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Twenty Five Guam Beaches

Figure 8-25. Seasonal variation at Asan Bay Beach Duration Curve Analysis A duration curve framework is used in Figure 8-26, Figure 8-27, and Figure 8-28 to relate bacteria concentrations to hydrologic conditions. These figures illustrate that the most exceedances occur under high flow conditions. As shown in Figure 8-26, over 50 percent of samples taken during high flow conditions were greater than the instantaneous WQS. Significant exceedances and elevated bacteria concentrations are also evident under all flow regimes as shown in Figure 8-27. The detailed water quality duration analysis identifies that the majority of the exceedances under high and moist flow conditions occur during the wet season or runoff events, whereas, exceedances under low flow conditions are dominated by dry weather events. Dry weather exceedances may be indicative of non-permitted point sources such as leaky sewers or failing septic tanks that are continuously discharging bacteria. The consistent presence of these sources is exemplified in Figure 8-28 where the dry season geomean nearly matches the wet season geomean in each flow regime. The duration curve analysis indicates that dry weather and wet weather sources may be contributing to elevated bacteria at Asan Bay Beach.

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Figure 8-26. Water quality duration analysis of Asan Bay Beach

Figure 8-27. Detailed water quality duration analysis of Asan Bay Beach

Bacteria Total Maximum Daily Loads

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Figure 8-28. Wet versus dry seasonal analysis for Asan Bay Beach Potential Sources 5 The drainage area of Asan Bay Beach encompasses developed and vegetated cover (Figure 8-29 and Figure 8-30). Asan Point is zoned as military land and consists of mostly developed open-space. The rest of the drainage area falls under agricultural zoning. The immediate area draining to Asan Bay Beach is highly developed. This is the only area of the watershed that has a sewer and road network. The remaining inland portions of the watershed are undeveloped and consist of cultivated crop and evergreen forest cover. Some specific sources near Asan Bay Beach identified in Figure 8-29 include untreated sewage discharge, stormwater runoff, and a public restroom on Asan Point. These sources may independently affect local water quality, but may also contribute to the effects of stormwater runoff. Additional potential sources identified by Guam EPA include septic systems, runoff from highway systems, recreational activities, and river discharge (Table 8-8).

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Figure 8-29. Land cover and location of Asan Bay Beach relative to potential source areas Table 8-8. Beach specific potential source summary (Site N-14: Asan Bay Beach) Site ID

Source Name (notes)

Type Wastewater

Septic System

Stormwater

Highway maintenance and Runoff

N-14 Recreation and Other

Recreation and Tourism Activities River discharge

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-30. Location of Asan Bay Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Asan Bay Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, demonstrate that bacteria levels elevate in the wet season even though dry season concentrations remain high (Figure 8-25). Duration curve analyses confirm that wet-season and runoff events dominate the exceedances observed under moist and high flow conditions (Figure 8-27). These analyses also illustrate a significant number of elevated concentrations during the dry-season which are most notable under dry and low flow conditions. These water quality trends indicate that wet-weather sources and dry-weather sources are contributing to the bacteria concentrations observed during both dry and wet seasons. Wetweather sources such as stormwater runoff and SSOs most frequently occur during the wet season and often result in the highest bacteria concentrations. Dry-weather sources, on the other hand, include septic systems, untreated sewage discharges, and faulty sewer mains which can directly impact waters at any time or significantly enhance the effects of stormwater runoff. Dry-weather sources have the most severe impacts to water quality during the dry season or dryweather. The technical analyses presented in this assessment of Asan Bay Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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Twenty Five Guam Beaches

TMDL Components Table 8-9 presents the TMDL for Asan Bay Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-9 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-9. TMDL summary (Site N-14: Asan Bay Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

207

Instantaneous

104

2,357

340

241

124

202

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-10 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-10. Reductions required to meet the TMDL (Site N-14: Asan Bay Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

85% 82%

47% 79%

3% 57%

--19%

--35%

83% 96%

34% 69%

16% 47%

-----

30% 69%

Note: --- indicates no reductions required for this condition

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8.4. Piti Bay (N-15) Piti Bay (RBMP site N-15) is in the northern Guam watershed and located north of Apra Harbor. On the shore of Piti Bay is Underway Observatory and Fish Eye Visitor Center where visitors can view the islandâ&#x20AC;&#x2122;s underwater wonders, including coral reefs. A portion of this area is a marine preserve known as the Piti Bomb Holes where fishing is now prohibited. As a result of the prohibition, fish and other sea life are abundant, making the waters popular among divers and snorkelers. Figure 8-31shows the location of Piti Bay and an aerial view of the area.

Figure 8-31. Location of Piti Bay relative to other TMDL sites Data collected weekly at the Piti Bay site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-32, there is a beach advisory 90 percent of the time based on data provided since 2001. This frequency of beach advisories poses a significant public health issue.

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Figure 8-32. Beach advisory frequency at Piti Bay The extent of bacteria present at Piti Bay from 2001 through 2011 is presented in Figure 8-33 as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards nearly every year with the rolling geomean falling below the geomean WQS in 2005 and 2006.The geometric mean of all individual samples was 24 counts /100 mL, while the 75th and 90th percentiles were 41 and 231 counts /100 mL, respectively.The rolling geomean ranges from 9 to 256 counts/100 mL (Figure 8-33). Although Figure 8-33 depicts some observations nearing 10,000 counts/100 mL, the relatively low 90th percentile and maximum average rolling geomean confirm that those are isolated events and not a consistent occurrence at Piti Bay.

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Figure 8-33. Enterococci data analysis at Piti Bay Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Piti Bay is illustrated in Figure 8-34. Although maximum observed concentrations exceeded the instantaneous WQS every year, the central tendency of bacteria concentrations on a yearly basis generally fell below 100 counts/100 mL (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS). As shown, 75 percent of the samples on a yearly basis fell below the instantaneous WQS with the exception of 2011 where the 75th percentile concentration fell above 104 counts/100 mL.

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Figure 8-34. Annual analysis of enterococcus data for Piti Bay Seasonal Analysis Seasonal variability of bacteria concentrations at Piti Bay is shown in Figure 8-35. As shown, maximum observed concentrations are observed on a monthly basis during both the wet and dry seasons. The seasonal analysis also demonstrates a typical trend of decreasing bacteria concentrations in the dry season months and increasing bacteria concentrations in the wet season months. The increasing concentrations observed in July, August, and September may be attributed to wet-weather sources near Piti Bay that contribute to elevated bacteria concentrations during storm events.

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Figure 8-35. Seasonal variation at Piti Bay Duration Curve Analysis A duration curve framework is used in Figure 8-36, Figure 8-37, and Figure 8-38 to relate bacteria concentrations to hydrologic conditions. These figures illustrate that the most exceedances occur under high flow conditions. As shown in Figure 8-36, over 50 percent of samples taken during high flow conditions were greater than the instantaneous WQS. Figure 8-37 identifies that many of those exceedances occur during the wet season or a stormwater runoff event. Exceedances under low, dry and mid-range flow conditions, however, were fewer and occurred under a mix of wet weather and dry weather conditions (Figure 8-37). A closer examination of seasonal effects in Figure 8-38 illustrates that dry season events had greatest influences in exceedances under high flow events suggesting that these observations were often related to stormwater runoff events occurring during the dry months. The typical variability in wet season events further confirms that elevated bacteria concentrations in Piti Bay may be attributed to stormwater runoff issues. The magnitude of these concentrations, however, indicate that there may be wastewater sources present influencing stormwater quality and resulting in concentrations between 1,000 and 10,000 counts/ 100 mL.

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Figure 8-36. Water quality duration analysis of Piti Bay

Figure 8-37. Detailed water quality duration analysis of Piti Bay

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Figure 8-38. Wet versus dry seasonal analysis for Piti Bay Potential Sources 5 There is mixed land cover within the drainage area of Piti Bay (Figure 8-39). High-intensity and open space development can be found along the shoreline as well as inland from the Piti Bay site. Vegetated cover, primarily evergreen forest, is found right outside the shoreline, while cultivated crop cover is found further inland in the upper portions of the watershed. Zoning areas illustrated in Figure 8-40 demonstrate that military lands are located east of Piti Bay and single-family units and planned unit developments coincide with the developed areas in Figure 8-39. As shown in Figure 8-40, the residential inland development sewer line is connected to the main sewer line along the coast. In addition to this coastal sewer line, Figure 8-39 shows five non-sewered buildings, an untreated sewage discharge, and two public restrooms in the Piti Bay vicinity. Guam EPA staff has also identified stormwater runoff, recreational/tourism activities, and river discharge as potential sources of bacteria (Table 8-11).

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Figure 8-39. Land cover and location of Piti Bay relative to potential source areas Table 8-11. Beach specific potential source summary (Site N-15: Piti Bay) Site ID

Source Name (notes)

Type Wastewater

Septic systems

Stormwater

Stormwater runoff

N-15 Recreation and Other

Recreational and Tourism Activities River discharge

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Figure 8-40. Location of Piti Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Piti Bay is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed between the wet weather months of July, August, and September (Figure 8-35). Even under lowflow conditions, wet-season events and runoff events have resulted in concentrations exceeding the water quality standards (Figure 8-37). These trends illustrate that stormwater runoff may be influencing the bacteria levels in Piti Bay. Other sources in the area that may be contributing to the bacteria levels include wastewater sources, such as septic systems and public restrooms, and recreational and tourism activities occurring in and present around Piti Bay. The technical analyses presented in this assessment of Piti Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-12 presents the TMDL for Piti Bay, identifying the loading capacity expressed as concentrationbased values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-12 also shows the observed concentrations associated with each

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flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-12. TMDL summary (Site N-15: Piti Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

1016

145

118

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-13 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-13. Reductions required to meet the TMDL (Site N-15: Piti Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

85% 82%

10% 70%

--13%

-----

52% 90%

-----

--6%

-----

--44%

Note: --- indicates no reductions required for this condition

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8.5. Santos Memorial Park Beach (N-16) Santos Memorial Park (RBMP site N-16), located in Piti, Guam, is part of the northern Guam watershed. The Masso River flows through the west side of the park and empties into Piti Bay. The park is named in honor of Senator Angel Leon Guerrero Santos who was a Chamorro rights activist and founding member of Nasion Chamoru, an indigenous activist group. The United Seamanâ&#x20AC;&#x2122;s Service (RBMP site N-17) is located to the west of the park. Figure 8-41shows the location of Santos Memorial Park and an aerial view of the area. No beach advisory data were available in the BEACON 2.0 database for Santos Memorial Park Beach (USEPA, 2012).

Figure 8-41. Location of Santos Memorial Park Beach relative to other TMDL sites The extent of bacteria present at Santos Memorial Park from 2001 through 2011 is presented in Figure 8-42 as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards every year with the lowest concentrations occurring in 2005and 2006. The geometric mean of all individual samples was 50 counts /100 mL, while the 75th and 90th percentiles were 166 and 583counts /100 mL, respectively. The high 75th and 90th percentile concentrations demonstrate a significant number of high bacteria concentrations at Santos Memorial Park. The rolling geomean ranged from 9 to 609 counts/100 mL, demonstrating significant exceedances at times.

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Figure 8-42. Enterococci data analysis at Santos Memorial Park Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Santos Memorial Park Beach (Figure 8-43) shows that maximum observed concentrations exceeded the instantaneous WQS every year.With the exception of 2005 and 2006, 25 percent of the data on a yearly basis exceeded the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared to the instantaneous WQS). Since 2006, bacteria levels have been on the rise with the highest median of bacteria concentrations occurring in 2011.

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Figure 8-43. Annual analysis of enterococcus data for Santos Memorial Park Beach Seasonal Analysis A seasonal analysis of enterococci data for Santos Memorial Park Beach is presented in Figure 8-44.As shown, maximum observed concentrations are observed on a monthly basis during bothwet and dry seasons. Elevated concentrations during the wet season months compared to dry season months is an evident trend in the seasonal analysis. Although more exceedances are observed during the wet season, instantaneous dry season concentrations remain near the instantaneous WQS. On a monthly basis, at least 25 percent of samples exceed the instantaneous WQS every month of the wet season. The most critical months during the wet season are July through October.

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Figure 8-44. Seasonal variation at Santos Memorial Park Beach Duration Curve Analysis A duration curve framework is used in Figure 8-45, Figure 8-46, and Figure 8-47 to relate bacteria concentrations to hydrologic conditions. These figures confirm that most exceedances occur under high and moist flow conditions. As shown in Figure 8-45, over 25 percent of samples taken during high flow, moist flow, and mid-range flow conditions are greater than the instantaneous WQS. Many of these midrange to high flow exceedances occur during wet season or stormwater runoff events, as identified in Figure 8-46. Several runoff events have occurred during the dry season, which is a result of a rainfall event washing bacteria bound particles off of surfaces and into receiving waterbodies (Figure 8-46 and Figure 8-47). In addition to runoff and wet season events, a number of dry weather events have also been reported to exceed water quality standards in low flow to moist flow conditions suggesting the presence of continuous bacteria input such as septic systems, wastewater discharges, or leaky sewer mains. Overall, rainfall events during both wet and dry seasons as well as potential wastewater sources may be influencing the presence of bacteria at Santos Memorial Park.

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Figure 8-45. Water quality duration analysis of Santos Memorial Park Beach

Figure 8-46. Detailed water quality duration analysis of Santos Memorial Park Beach

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Figure 8-47. Wet versus dry seasonal analysis for Santos Memorial Park Beach Potential Sources 5 The drainage area to Santos Memorial Park Beach consists of mixed land cover ranging from high intensity developed land along the shore to evergreen forest and cultivated crop cover within 10 miles inland from the coast (Figure 8-48). Figure 8-49illustrates zoning for one-family dwellings in the immediate vicinity and extensive military land zones south of the Santos Memorial Park Beach site. An additional planned unit development is located inland from the shore. Both residential neighborhoods have a road and sewer line network (Figure 8-49)which may serve as stormwater and wastewater sources of bacteria, respectively. Several non-sewered buildings have been identified along the shore (Figure 8-48), which may also pose as wastewater sources of bacteria. Other potential sources in the area have been identified by Guam EPA staff to include a historic confined animal feedlot and river discharge (Table 8-14).

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Figure 8-48. Land cover and location of Santos Memorial Park Beach relative to potential source areas Table 8-14. Beach specific potential source summary (Site N-16: Santos Memorial Park Beach) Site ID

Source Name (notes)

Type Wastewater

Septic systems

Stormwater

Stormwater runoff

N-16

Historical Confined Animal Feedlot (chicken) Other River discharge

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Figure 8-49. Location of Santos Memorial Park Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Santos Memorial Park Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the most exceedances occur during the wet season, however, elevated bacteria levels also occur in the dry season (Figure 8-44). According to the duration curve analysis, most of the high and moist flow exceedances were a result of a wet-season event or stormwater runoff, and dry-event exceedances were evident under all flow regimes (Figure 8-46). These trends strongly suggest that stormwater issues may be influencing water quality. The consistently high concentrations under low flow conditionsmay also be an indicator of wastewater sources in the vicinity further contributing to bacteria levels. The presence of stormwater runoff and potential wastewater sources such as septic systems, sewer lines, and a public restroom have been identified as potential sources in the Santos Memorial Park Beach that may be compromising water quality. The technical analyses presented in this assessment of Santos Memorial Park Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-15 presents the TMDL for Santos Memorial Park Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-15 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-15. TMDL summary (Site N-16: Santos Memorial Park Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

203

Instantaneous

104

2,088

629

305

167

206

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-16 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-16. Reductions required to meet the TMDL (Site N-16: Santos Memorial Park Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

91% 95%

47% 82%

--47%

--34%

--42%

82% 95%

51% 84%

26% 78%

--39%

--42%

Note: --- indicates no reductions required for this condition

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8.6. United Seamen’s Service (N-17) United Seaman’s Service (RBMP site N-17) located on the shore of Piti Bay in the northern Guam watershed. The site has been providing service for American and International seafarers since World War II. It is one of seven port centers worldwide which provide recreation, communications, counseling, food, beverages, gift shops, and health services. Figure 8-50shows the location of United Seaman’s Service and an aerial view of the area.

Figure 8-50. Location of United Seamen’s Service relative to other TMDL sites Data collected weekly at the United Seamen’s Service site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-51, 9 percent of beach days at United Seamen’s Service had a beach advisory based on data provided since 2001 and does not pose a significant public health issue, when compared with other area beaches.

100

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Figure 8-51. Beach advisory frequency at United Seamen’s Service The extent of bacteria present at United Seamen’s Service from 2001 through 2011 is presented inFigure 8-52 as instantaneous and five-week geomean samples of enterococci data. As shown, exceedances are most prevalent in 2001 through 2004 and 2010 through 2011.The geometric mean of all individual samples was 13 counts /100 mL, while the 75th and 90th percentiles were 10 and 35counts /100 mL, respectively.The rolling geomean ranges from 9 to 96 counts/100 mL (Figure 8-52). Overall, exceedances at United Seaman’s Service are comparatively infrequent and not severe in magnitude.

101

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Figure 8-52. Enterococci data analysis at United Seamenâ&#x20AC;&#x2122;s Service Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the United Seamanâ&#x20AC;&#x2122;s Service site is presented in Figure 8-53. As shown,the central tendency of bacteria concentrations falls well below the water quality standards every year of the study period. Although infrequent, maximum concentrations observed did occur most years for the exception of 2004, 2005, and 2007 (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS).

102

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Figure 8-53. Annual analysis of enterococcus data for United Seamenâ&#x20AC;&#x2122;s Service Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. The seasonal variability of bacteria concentrations at the United Seamenâ&#x20AC;&#x2122;s Service site is presented in Figure 8-54. Since bacteria concentration ranges were relatively small at this site, distinct trends or differences between the two seasons is difficult to draw. One trend that is evident from the seasonal analysis is that the greatest concentrations occur during the wet season months, specifically September and October.

103

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Figure 8-54. Seasonal variation at United Seamenâ&#x20AC;&#x2122;s Service Duration Curve Analysis A duration curve framework is used in Figure 8-55, Figure 8-56, and Figure 8-57 to relate bacteria concentrations to hydrologic conditions. These figures confirm that exceedances occur under all flow regimes. The highest bacteria concentrations occur under high and moist flow conditions (Figure 8-55), many of which are a result of a wet season event (Figure 8-56). Exceedances during the dry season have also occurred under all flow regimes which can be reflective of rainfall events that wash bacteria-bound particles off of surfaces and into the receiving waters (Figure 8-57). Although exceedances are relatively infrequent, the detailed water quality duration curve analysis concludes that stormwater runoff may be contributing to the bacteria levels during both wet- and dry seasons.

104

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Figure 8-55. Water quality duration analysis of United Seamenâ&#x20AC;&#x2122;s Service

Figure 8-56. Detailed water quality duration analysis of United Seamenâ&#x20AC;&#x2122;s Service

105

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Figure 8-57. Wet versus dry seasonal analysis for United Seamenâ&#x20AC;&#x2122;s Service Potential Sources 5 The drainage area to the United Seamenâ&#x20AC;&#x2122;s Service site consists of mixed land cover ranging from high intensity developed land along the shore to evergreen forest and cultivated crop cover 10 miles inland (Figure 8-58). Figure 8-59illustrates one-family dwelling in the immediate vicinity and extensive military land zones south of the United Seamenâ&#x20AC;&#x2122;s Service site. An additional planned unit development is located inland from the shore. Both residential neighborhoods have a road and sewer line network (Figure 8-59) that may serve as stormwater and wastewater sources of bacteria, respectively. According to Figure 8-58, stormwater runoff, a public restroom, and several non-sewered buildings have been identified along the shore which may also pose as wastewater sources of bacteria. Guam EPA staff have also identified recreational and tourism activities as potential sources of bacteria (Table 8-17).

106

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Figure 8-58. Land cover and location of United Seamenâ&#x20AC;&#x2122;s Service relative to potential source areas Table 8-17. Beach specific potential source summary (Site N-17: United Seamenâ&#x20AC;&#x2122;s Service) Site ID

Type

N-17

Recreation and Other

Source Name (notes) Recreational and tourism activities

107

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Figure 8-59. Location of United Seamen’s Service relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guam’s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at the United Seamen’s Service site is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during the wet season (Figure 8-54). Water quality duration analyses show that the highest concentrations occur under high and moist flow conditions and are often a result of wet-weather events or stormwater runoff events (Figure 8-56). These trends suggestthat stormwater issues are impacting the waters at United Seamen’s Service. Dry-weather exceedances under most flow regimes can also be a product of stormwater sources but may also indicate the presence of local wastewater sources. Potential sources identified in the area including septic systems, sewer mains, and stormwater runoff points are consistent with the water quality trends present at United Seamen’s Service. Recreational and tourism activities contributing to elevated bacteria may also be a potential source during both wet- and dry-seasons.

TMDL Components Table 8-18 presents the TMDL for Unites Seaman’s Service, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-18 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

108

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Table 8-18. TMDL summary (Site N-17: United Seamenâ&#x20AC;&#x2122;s Service) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-19 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-19. Reductions required to meet the TMDL (Site N-17: United Seamanâ&#x20AC;&#x2122;s Service) Flow Condition (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

--81%

-----

Note: --- indicates no reductions required for this condition

109

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8.7. Outhouse Beach (N-18) Outhouse Beach (RBMP site N-18) is a common dive site inside Apra Harbor in the northern Guam watershed. It is east of another diving spot, Family Beach. Outhouse beach is a popular spot for SCUBA certification dives. The beach is steep and primarily consists of large pebbles. Although there is little to no reef and sea life there, the weather is generally diveable due to its location inside Apra Harbor. Outhouse Beach is classified as M-3 waters which have the same geomean WQS as M-2 waters, but a higher instantaneous WQS of 276 counts/100 mL. Figure 8-60 shows the location of Outhouse Beach and an aerial view of the area.

Figure 8-60. Location of Outhouse Beach relative to other TMDL sites Data collected weekly at the Outhouse Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters).As shown in Figure 8-61, based on data provided since 2001, 8 percent of beach days at Outhouse Beach had a beach advisory based on data provided since 2001 and does not pose a significant public health issue compared to other regional beaches.

110

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Figure 8-61. Beach advisory frequency at Outhouse Beach The extent of bacteria present at Outhouse Beach from 2001 through 2011 is presented in Figure 8-62 as instantaneous and five-week geomean samples of enterococci data. The instantaneous WQS displayed in Figure 8-62 reflects the standard for M-2 waters, 104 counts/100 mL, which is more stringent than the instantaneous WQS for M-3 waters. This standard is used in the analyses as it is more conservative and is associated with the criteria threshold used for beach advisories.As shown in Figure 8-62, the greatest variability in bacteria concentrations occurred in years prior to 2005. Since then, instantaneous WQS exceedances were sparse and generally remained below 1,000 counts/100 mL. Comparatively, rolling geomean exceedances rarely occurred during the period of record. The geometric mean of all individual samples was 13 counts /100 mL, while the 75th and 90th percentiles were 10 and 31 counts /100 mL, respectively.The rolling geomean ranges from 9 to 117 counts/100 mL (Figure 8-62).

111

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Figure 8-62. Enterococci data analysis at Outhouse Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Outhouse Beach is presented in Figure 8-63. Although maximum observed concentrations exceeded the instantaneous WQS every year, the central tendency of bacteria concentrations fell well below 100 counts/100 mL every year (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS).

112

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Figure 8-63. Annual analysis of enterococcus data for Outhouse Beach Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. The seasonal variability of bacteria concentrations at Outhouse Beach is presented in Figure 8-64. Distinct seasonal trends are difficult to conclude given the consistently low variability of bacteria concentrations at this site. One distinction, however, that is evident from the seasonal analysis is that the greatest concentrations occur during the wet season months. These high bacteria concentrations, although infrequent, can be a result of heavy rainfall events introducing bacteria-bound particles to the receiving waters.

113

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Figure 8-64. Seasonal variation at Outhouse Beach Duration Curve Analysis A duration curve framework is used in Figure 8-65, Figure 8-66, and Figure 8-67 to relate bacteria concentrations to hydrologic conditions. These figures confirm that exceedances occur under nearly all flow regimes with the most exceedances occurring in moist and high flow conditions (Figure 8-65). Exceedances in these analyses refer to exceedances of the instantaneous WQS of 104 counts/100 mL, which is more stringent than the WQS applied to M-3 waters. The growing number of exceedances with increased flow conditions suggests that stormwater issues and stormwater runoff may be significant contributors to bacteria levels at Outhouse Beach. The few dry-weather exceedances in all the flow regimes and particularly the moist flow regime are also indicative of stormwater influences (Figure 8-66 and Figure 8-67). This is expected since long antecedent periods of no rainfall causes the build-up of bacteria-bound particles to be washed-off in a dry season rainfall event. Although exceedances are relatively infrequent, the detailed water quality duration curve analysis concludes that stormwater runoff may be contributing to the bacteria levels during both wet- and dry seasons.

114

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Figure 8-65. Water quality duration analysis of Outhouse Beach

Figure 8-66. Detailed water quality duration analysis of Outhouse Beach

115

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Figure 8-67. Wet versus dry seasonal analysis for Outhouse Beach Potential Sources 5 The drainage area to Outhouse Beach is small and predominantly covered by high-intensity developed land with some shrubbery and bare land (Figure 8-68).The only zoning in the area is for commercial use, which attracts tourists and recreational users to the area (Figure 8-69). Source assessment of permitted facilities in Section 5.1 identified that the Guam Shipyard facility has a discharge permit for bacteria. The Shipyard outfalls are on the southern shores of Apra Harbor, and discharge may have the potential to reach northern shore beaches as a result of tidal circulation (Figure 5-2). Specific sources of bacteria that have been identified in the vicinity include portable toilets, stormwater runoff, and a sewage holding tank. Specific potential sources identified by Guam EPA staff include septic systems and stormwater runoff(Table 8-20).

116

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Figure 8-68. Land cover and location of Outhouse Beach relative to potential source areas Table 8-20. Beach specific potential source summary (Site N-18: Outhouse Beach) Site ID

N-18

Source Name (notes)

Type Wastewater

Septic systems

Stormwater

Stormwater runoff

Wastewater

Permitted discharge from an Industrial Point Source

117

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Figure 8-69. Location of Outhouse Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). Although Outhouse Beach is classified as M-3 waters, using M-2 WQS as a numeric target is more stringent and is associated to the threshold criteria for beach advisories, thereby most conservative in regards to public health. The relationship between this target and potential sources at Outhouse Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during the wet season (Figure 8-64). Water quality duration analyses show that the highest concentrations occur under high and moist flow conditions and are often a result of wet-weather events or stormwater runoff events (Figure 8-66). These trends suggest a strong influence of stormwater issues impacting the waters at Outhouse Beach. Dry-weather exceedances under most flow regimes can be a product of stormwater sources but may also hint the presence of local wastewater sources. Potential sources identified in the area including septic systems, public restrooms, and stormwater runoff points are consistent with the water quality trends present at Outhouse Beach. The technical analyses presented in this assessment of Outhouse Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

118

Bacteria Total Maximum Daily Loads

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TMDL Components Table 8-21 presents the TMDL for Outhouse Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-2). Because this is an M-3 beach, the instantaneous WQS is 276 counts / 100 mL. These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-21 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-21. TMDL summary (Site N-18: Outhouse Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

276

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-22 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the geomean TMDL concentrations and the instantaneous M-2 WQS, which is used for beach assessments. The more stringent M-2 WQS is used for this analysis to be more protective of public health and to reduce the beach advisory frequencies, thereby achieving the designated uses. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-22. Reductions required to meet the TMDL and M-2 WQS (Site N-18: Outhouse Beach) Flow Condition (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

--83%

--38%

-----

Note: --- indicates no reductions required for this condition

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8.8. Family Beach (N-19) Family Beach (RBMP site N-19) is west of Outhouse Beach in Apra Harbor. Unlike Outhouse Beach, Family Beach is a more favorable diving spot as it is fairly lit with moderately well-developed corals and moderately abundant sea life. A canyon runs parallel to the beach providing an attractive spot for divers. Figure 8-70shows the location of Family Beach and an aerial view of the area.

Figure 8-70. Location of Family Beach relative to other TMDL sites Data collected weekly at the Family Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-71, 6 percent of beach days at Family Beach since 2001 had a beach advisory.Conditions at this site, as demonstrated by the number of beach advisories, do not pose a significant public health issue when compared to other beaches in the region.

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Figure 8-71. Beach advisory frequency at Family Beach Consistent with the low number of beach advisories, the instantaneous and five-week geomean samples of enterococci data from 2001 through 2011 (Figure 8-72) also illustrate low bacteria levels observed at Family Beach. From 2002 through 2004, a high frequency of elevated concentrations occurred; however, since then there has been only a few instances where WQS were exceeded.The geometric mean of all individual samples was 11 counts /100 mL, while the 75th and 90th percentiles were 9 and 10 counts /100 mL, respectively.The rolling geomean ranges from 9 to 49 counts/100 mL (Figure 8-72).

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Figure 8-72. Enterococci data analysis at Family Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Family Beach is presented in Figure 8-73, where maximum observed concentrations exceeded the instantaneous WQS in only four years of the study period. The central tendency of bacteria concentrations are about 10 counts/100 mL every year (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS).

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Figure 8-73. Annual analysis of enterococcus data for Family Beach Seasonal Analysis Figure 8-74 presents a seasonal analysis of bacteria concentrations at Family Beach to evaluate patterns during the dry- and wet-weather seasons. Given the low variability of bacteria concentrations at this site, distinct seasonal trends are difficult to conclude. Maximum observed concentrations exceeding the instantaneous WQS are evident in both seasons suggesting that potential sources of bacteria are not influenced by season. Elevated bacteria levels may be attributed to rainfall events which occur in either season.

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Figure 8-74. Seasonal variation at Family Beach Duration Curve Analysis A duration curve framework is used in Figure 8-75,Figure 8-76, and Figure 8-77 to relate bacteria concentrations to hydrologic conditions. These figures confirm that exceedances, although infrequent, occur under dry to high flow conditions (Figure 8-75). The majority of these exceedances are a result of a wet season event or stormwater runoff event suggesting that elevated bacteria concentrations are associated with rainfall events and stormwater issues (Figure 8-76 and Figure 8-77). The few dry weather exceedances can also be attributed to rainfall events that occur after long antecedent periods of no rainfall. Overall, although few in number, bacteria exceedances at Family Beach are related to stormwater runoff as concluded by the duration curve analysis.

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Figure 8-75. Water quality duration analysis of Family Beach

Figure 8-76. Detailed water quality duration analysis of Family Beach

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Figure 8-77. Wet versus dry seasonal analysis for Family Beach Potential Sources 5 The drainage area to Family Beach is small and predominantly covered by shrubbery, bare land, and some developed commercial land (Figure 8-78and Figure 8-79).The commercial land use and barren land make Family Beach and ideal attraction for tourists and recreational users. There are no sewer lines present in the area, but a portable toilet is identified to manage wastewater (Figure 8-78). Source assessment of permitted facilities in Section 5.1 identified that the Guam Shipyard facility has a discharge permit for bacteria. The Shipyard outfalls are on the southern shores of Apra Harbor, and discharge may have the potential to reach northern shore beaches as a result of tidal circulation (Figure 5-2). Guam EPA staff has also identified recreational and tourism activities as potential sources of bacteria to Family Beach (Table 8-23).

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Figure 8-78. Land cover and location of Family Beach relative to potential source areas Table 8-23. Beach specific potential source summary (Site N-19: Family Beach) Site ID

Type Wastewater

N-19

Recreation and Other

Source Name (notes) Permitted discharge from an Industrial Point Source Recreational and Tourism activities

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Figure 8-79. Location of Family Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Family Beach is demonstrated through an analysis of water quality monitoring data at this site. Although, there are no strong seasonal trends, the water quality duration analysis identifies that most of the exceedances occur during wet-weather events or stormwater runoff events (Figure 8-76). Dry-weather exceedances, although minor in number, also illustrate stormwater influences after a rainstorm following long dry periods of time. These water quality trends suggest that elevated bacteria concentrations are likely from stormwater runoff and recreational activities present at Family Beach. The technical analyses presented in this assessment of Family Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-24 presents the TMDL for FamilyBeach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-24 also shows the observed concentrations

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associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-24. TMDL summary (Site N-19: Family Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-25 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions). For Family Beach, no reductions are currently required to meet WQS. As an antidegradation measure, the TMDL focuses on maintaining this situation and making additional improvements to reduce the number of beach advisory days.

Table 8-25. Reductions required to meet the TMDL (Site N-19: Family Beach) Flow Condition (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

-----

Note: --- indicates no reductions required for this condition

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8.9. Port Authority Beach (N-20) Port Authority Beach (RBMP site N-20) is located within Apra Harbor in the northern Guam watershed. It is east of and closer inland compared to Outhouse Beach and Family Beach. Also unlike Outhouse Beach and Family Beach, the Port Authority Beach is not a spot for divers or snorkelers. Port Authority Beach is classified as M-3 waters which have the same geomean WQS as M-2 waters, but a higher instantaneous WQS of 276 counts/100 mL. Figure 8-80shows the location of Port Authority Beach and an aerial view of the area.

Figure 8-80. Location of Port Authority Beach relative to other TMDL sites Data collected weekly at the Port Authority Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown inFigure 8-81, 10 percent of beach days at Port Authority Beach had a beach advisory since 2001. Conditions at this site, as demonstrated by the number of beach advisories compared to other regional beaches, do not pose a significant public health threat.

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Figure 8-81. Beach advisory frequency at Port Authority Beach The extent of bacteria present at Port Authority Beach from 2001 through 2011 is presented in Figure 8-82 as instantaneous and five-week geomean samples of enterococci data. As shown, instantaneous WQS exceedances occur nearly every year; whereas, rolling geomean exceedances are less frequent.These exceedances are relative to the instantaneous WQS for M-2 waters, 104 counts/100 mL, which is more stringent than the WQS for M-3 waters. This standard is used in the analyses as it is more conservative and is associated with the criteria threshold used for beach advisories. The geometric mean of all individual samples is 15 counts /100 mL, while the 75th and 90th percentiles were 20 and 63 counts /100 mL, respectively.The rolling geomean ranges from 9 to 91 counts/100 mL (Figure 8-82).

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Figure 8-82. Enterococci data analysis at Port Authority Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Port Authority Beach is illustrated in Figure 8-83. Although maximum observed concentrations exceeded the M-2 instantaneous WQS nearly every year, the central tendency of bacteria concentrations on a yearly basis generally fell well below 100 counts/100 mL (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the data presented in the boxplot can be compared with the instantaneous WQS).

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Figure 8-83. Annual analysis of enterococcus data for Port Authority Beach Seasonal Analysis Seasonal patterns of bacteria exceedances during dry- and wet-weather seasons can be examined in Figure 8-84 for Port Authority Beach.Although maximum observed concentrations have exceeded M-2 instantaneous WQS in both the wet- and dry- seasons, greater variability in bacteria concentrations is more prevalent in wet-season months. This high variability may be attributed to the frequent rainfall events during the wet-season suggesting that stormwater issues and stormwater runoff may be potential sources of elevated bacteria in Port Authority Beach.

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Figure 8-84. Seasonal variation at Port Authority Beach Duration Curve Analysis A duration curve framework is used in Figure 8-85, Figure 8-86, and Figure 8-87 to relate bacteria concentrations to hydrologic conditions. These figures confirm that exceedances occur under all flow regimes. Exceedances in these analyses refer to exceedances of the instantaneous WQS of 104 counts/100 mL, which is more stringent than the WQS applied to M-3 waters. Most of these exceedances are a result of a wet season event or stormwater runoff event suggesting that elevated bacteria concentrations are associated with rainfall events and stormwater issues (Figure 8-76 and Figure 8-77). The few dry weather exceedances can also be attributed to rainfall events that occur after long antecedent periods of no rainfall. Despite the low overall number of exceedances at Port Authority Beach, bacteria exceedances are related to stormwater runoff as concluded by the duration curve analysis.

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Figure 8-85. Water quality duration analysis of Port Authority Beach

Figure 8-86. Detailed water quality duration analysis of Port Authority Beach

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Figure 8-87. Wet versus dry seasonal analysis for Port Authority Beach Potential Sources 5 The drainage area to Port Authority Beach consists of a mix of land uses. Although mostly covered by vegetation and wetlands, open-space and high-intensity developed land is present to support the commercial zoning (Figure 8-88and Figure 8-89). As shown in Figure 8-89, the entire drainage area has been zoned for commercial use regardless of cover. No sewer network is present in the drainage area, but a small road network may serve as an avenue for stormwater runoff (Figure 8-88andFigure 8-89). Source assessment of permitted facilities in Section 5.1 identified that the Guam Shipyard facility has a discharge permit for bacteria. The Shipyard outfalls are on the southern shores of Apra Harbor, and discharge may have the potential to impact Port Authority Beach as a result of tidal circulation (Figure 5-2). Guam EPA staff has identified septic systems and an industrial point source as potential sources of bacteria to Port Authority Beach (Table 8-26).

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Figure 8-88. Land cover and location of Port Authority Beach relative to potential source areas Table 8-26. Beach specific potential source summary (Site N-20: Port Authority Beach) Site ID

Source Name (notes)

Type Septic systems

N-20

Wastewater

Industrial point source (GPA) Permitted discharge from an Industrial Point Source

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Figure 8-89. Location of Port Authority Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). Although Port Authority Beach is classified as M-3 waters, using M-2 WQS as a numeric target is more stringent and is associated to the threshold criteria for beach advisories, thereby most conservative in regards to public health. The relationship between this target and potential sources at Port Authority Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, showthat the wet season demonstrates the greatest variability of bacteria levels (Figure 8-84). In addition, elevated bacteria concentrations occur under all flow conditions with the greatest exceedances occurring during the wet season or a runoff event (Figure 8-86). These water quality trends suggest that rainfall events and stormwater runoff may be influencing the bacteria levels present at Port Authority Beach. The road network, developed land cover, and little to no stormwater management all contribute to stormwater runoff at Port Authority Beach. The technical analyses presented in this assessment of Port Authority Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-27 presents the TMDL for Port Authority Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are

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presented in Table 7-2). Because this is an M-3 beach, the instantaneous WQS is 276 counts / 100 mL. These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-27 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-27. TMDL summary (Site N-20: Port Authority Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

276

117

104

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-28 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the geomean TMDL concentrations and the instantaneous M-2 WQS, which is used for beach assessments. The more stringent M-2 WQS is used for this analysis to be more protective of public health and to reduce the beach advisory frequencies, thereby achieving the designated uses. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-28. Reductions required to meet the TMDL and M-2 WQS(Site N-20: Port Authority Beach) Flow Condition (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

--23%

-----

23% 67%

Note: --- indicates no reductions required for this condition

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8.10. Togcha Beach â&#x20AC;&#x201C; Namo River (S-02) Togcha Beach near Namo River (RBMP site S-02), located on the west coast of Southern Guam, is one of three Togcha Beach sites. The Namo River site is the most northern site of the three on the northern edge of Agat village. Togcha Beach makes up the shoreline of Agat Bay. Figure 8-90shows the location of Togcha Beach near Namo River and an aerial view of the area.

Figure 8-90. Location of Togcha Beach near Namo River relative to other TMDL sites Beach advisory decisions for Togcha Beach near Namo River are made based on data collected at Agat Beach. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-91, 75 percent of beach days at Togcha Beach had a beach advisory based on data provided since 2001. This frequency of beach advisories is a significant public health issue and is in line with beach advisories in Agat Bay measured at Bangi Beach (RBMP site S-04).

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Figure 8-91. Beach advisory frequency at Togcha Beach near Namo River The extent of bacteria present at Togcha Beach near Namo River from 2001 through 2011 is presented in Figure 8-92 as instantaneous and five-week geomean samples of enterococci data. As illustrated, bacteria levels at this site are highly variable with exceedances of the instantaneous and geomean WQS occurring every year.The geometric mean of all individual samples was 33 counts /100 mL, while the 75th and 90th percentiles were 74 and 341 counts /100 mL, respectively.The rolling geomean ranges from 9 to 729 counts/100 mL (Figure 8-156).

Figure 8-92. Enterococci data analysis at Togcha Beach near Namo River 141

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Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Togcha Beach near Namo River is presented in Figure 8-93. Although maximum observed concentrations exceed the instantaneous WQS every year, the central tendency of bacteria concentrations generally falls below the WQS on a yearly basis (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS). The greatest number of exceedances per year occurred in 2009 and 2011 were 25 percent of the samples exceeded 104 counts/100 mL.

Figure 8-93. Annual analysis of enterococcus data for Togcha Beach near Namo River Seasonal Analysis A seasonal analysis of the data obtained at Togcha Beach near Namo River displays a trend between the wet- and dry-seasons. As shown in Figure 8-94, monthly medians of the wet season were generally higher than those of the dry season. Further, more exceedances were observed during the wet-season on a monthly basis as illustrated by 75th percentiles falling above the instantaneous WQS. Although, the seasonal analysis demonstratesmore exceedances and higher bacteria concentrations during the wetseason, maximum observed concentrations during the dry-season did exceed the instantaneous WQS on a monthly basis. Nonetheless, the sources of bacteria play a significant role during the wet-season months suggesting that stormwater issues may be contributing to the bacteria concentrations at Togcha Beach near Namo River.

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Figure 8-94. Seasonal variation at Togcha Beach near Namo River Duration Curve Analysis A duration curve framework is used in Figure 8-95, Figure 8-96, and Figure 8-97 to relate bacteria concentrations to hydrologic conditions. These figures confirm that most exceedances occur under high flow conditions. As shown in Figure 8-95, over 25 percent of samples taken during high flow conditions are greater than the instantaneous WQS. A detailed analysis explored in Figure 8-96 shows that nearly all exceedances under high flow conditions occur during the wet-season or a runoff event. Wet-season events, as well as dry-season events, are also responsible for exceedances under other flow conditions (Figure 8-96). The elevated wet-season levels compared to the dry-season levels in each flow regime (Figure 8-97) confirm that most exceedances are driven by wet-weather sources such as stormwater runoff and other stormwater related issues.

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Figure 8-95. Water quality duration analysis of Togcha Beach near Namo River

Figure 8-96. Detailed water quality duration analysis of Togcha Beach near Namo River

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Figure 8-97. Wet versus dry seasonal analysis for Togcha Beach near Namo River Potential Sources 5 The Togcha Beach site near Namo Riverhas an expansive drainage area that encompasses various vegetated covers (evergreen forest, cultivated crop, shrub), wetland cover, and developed cover (openspace and high intensity) (Figure 8-98). Zoning in the drainage area is also mixed as it includes industrial zoning in the lower portion of the drainage area and military use and agricultural use. The middle portion of the drainage area is primarily residential zoning such as one-family dwellings and planned unit dwellings (Figure 8-99). A road network is throughout the drainage area, but a sewer network is limited to the residential zones areas (Figure 8-98). Namo River flows throughout the drainage area and serves as a delivery mechanism for bacteria from upland sources to reach Togcha Beach. Several potential sources of bacteria are identified in Figure 8-98. In the immediate area of the site several point sources such as stormwater runoff and untreated sewage discharge are present. Inland and upstream of Namo River are several non-sewered buildings that line the river and road network. These non-sewered buildings are found in the areas zoned for agricultural use and single-family dwellings. In addition to these septic systems, a piggery is identified to be located within the single-family zoned area about 5 miles away from Namo River.A piggery may serve as a potential source of bacteria via stormwater runoff. Upland sources and wastewater sources such as sewer line breaks and SSOs have also been identified by Guam EPA staff as potential sources (Table 8-29).

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Figure 8-98. Land cover and location of Togcha Beach near Namo River relative to potential source areas Table 8-29. Beach specific potential source summary (Site S-02: Togcha Beach near Namo River) Site ID

Source Name (notes)

Type Wastewater

S-02 Other

Sewer line block/break SSO River discharge

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Figure 8-99. Location of Togcha Beach near Namo River relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Togcha Beach near Namo River is demonstrated through an analysis of water quality monitoring data at this site. A seasonal analysis, for example, reveals that the most exceedances and highest concentrations occur during the wet-season (Figure 8-94). In addition, exceedances under high flows are dominated by wet-season and runoff events suggesting the influence of wet-weather sources (Figure 8-96). Upland sources such as a piggery, developed land cover, and road networks may contribute to bacteria levels via stormwater runoff. Other sources such as septic systems and leaky sewer lines identified in the area may also be introduced to receiving waters and exacerbated during wet-weather events. The significant number of beach advisories at Togcha Beach is likely the result of elevated bacteria levels from these sources. The technical analyses presented in this assessment of Togcha Beach near Namo River describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-30 presents the TMDL for Togcha Beach near Namo River, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity

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and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-30 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-30. TMDL summary (Site S-02: Togcha Beach near Namo River) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

150

Instantaneous

104

3,375

312

131

429

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-31 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-31. Reductions required to meet the TMDL (Site S-02: Togcha Beach near Namo River) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

69% 98%

--58%

--15%

-----

--4%

78% 97%

14% 71%

--20%

3% 58%

75% 95%

Note: --- indicates no reductions required for this condition

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8.11. Togcha Beach â&#x20AC;&#x201C; Agat Bay (S-03) Togcha Beach near Agat Park (RBMP site S-03) is one of three Togcha Beach sites on the west coast of Southern Guam. The park is a historical site that honors all who participated in the Liberation of Guam after World War II. Figure 8-100shows the location of Togcha Beach near Agat Park Beach and an aerial view of the area.

Figure 8-100. Location of Agat Bay relative to other TMDL sites Data collected weekly at Togcha Beach near Agat Park are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-101, 75 percent of beach days at Togcha Beach had a beach advisory based on data provided since 2001. This frequency of beach advisories is a significant public health issue and is in line with beach advisories in Agat Bay measured at Bangi Beach (RBMP site S-04).

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Figure 8-101. Beach advisory frequency at Agat Bay The high variability of bacteria concentrations observed at Togcha Beach near Agat Park from 2001 through 2011is presented in Figure 8-102as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards every year. The geometric mean of all individual samples was 33 counts /100 mL, while the 75th and 90th percentiles are85 and 339 counts /100 mL, respectively.The rolling geomean ranges from 9 to 860 counts/100 mL (Figure 8-102).

Figure 8-102. Enterococci data analysis at Agat Bay 150

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Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Togcha Beach near Agat Park site (Figure 8-103) shows that maximum observed concentrations exceeded the instantaneous WQS every year. The years with the greatest number of instantaneous WQS exceedances include 2006, 2010, and 2011 where 25 percent of the samples taken per year exceeded the WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS).

Figure 8-103. Annual analysis of enterococcus data for Agat Bay Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. Figure 8-104 shows a seasonal trend where wet-season months illustrated elevated bacteria concentrations compared to those of the dry-season months. The most exceedances occur in July through October where at least 25 percent of the samples on a monthly basis exceeded the instantaneous WQS. Although exceedances are not as common in the dry season, the elevated bacteria levels present during these months may be attributed to local wastewater sources. This analysis indicates that wet-weather sources as well as dry-weather sources may be playing a role in the bacteria levels observed at Togcha Beach near Agat Park.

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Figure 8-104. Seasonal variation at Agat Bay Duration Curve Analysis A duration curve framework is used in Figure 8-105, Figure 8-106, and Figure 8-107 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the highest concentrations are observed under high flow conditions followed by low flow conditions and moist flow conditions. Concentrations greater than 10,000 counts/100 mL occurred exclusively under high flow conditions and over 25 percent of samples under high flow conditions exceeded the instantaneous WQS (Figure 8-105).A detailed analysis (Figure 8-106) confirms that exceedances under high flow conditions are predominantly observances during the wet-season or a runoff event. Figure 8-106also demonstrates that dry-season exceedances, although to a lesser extent, did occur under all flow regimes. These dry-weather exceedances can be attributed to either rainfall events washing the build-up of bacteria-bound particles after long periods of no rainfall or the influence of wastewater sources. The influence of stormwater runoff on bacteria levels is also evident in Figure 8-107 where the wet-season geomeans were higher than the dry-season geomeans in nearly all the flow regimes. These trends suggest that bacteria from wet weather and dry weather sources may be influencing the water quality at Togcha Beach near Agat Park.

152

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Figure 8-105. Water quality duration analysis of Agat Bay

Figure 8-106. Detailed water quality duration analysis of Agat Bay

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Figure 8-107. Wet versus dry seasonal analysis for Agat Bay Potential Sources 5 The drainage area to Togcha Beach near Agat Park is a small coastal drainage area that is predominantly covered by high-intensity and open-space developed land (Figure 8-108). Inland from the shore are Palustrine wetlands surrounded by evergreen forest and other natural vegetation. The majority of the area is zoned for multiple dwellings, single-family dwellings, and commercial use (Figure 8-109). Agricultural land has been zoned for the areas containing the Palustrine wetlands and surrounding vegetation. Non-sewered buildings are not identified in the drainage area and a sewer line network does run through the residential neighborhoods of the drainage area (Figure 8-109). A road network is also present in the drainage area and along the shore which can serve as a favorable transport mechanism for stormwater runoff from the developed land cover. As shown in Figure 8-108 and captured in Table 8-32, untreated sewage discharge as well as stormwater runoff have been identified as specific sources of bacteria near the monitoring site that may be compromising the water quality at Togcha Beach near Agat Park.

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Figure 8-108. Land cover and location of Agat Bay relative to potential source areas Table 8-32. Beach specific potential source summary (Site S-03: Agat Bay) Site ID S-03

Source Name (notes)

Type Wastewater

Sewer line block/break

Stormwater

Stormwater runoff

Note: The sources identified in this table were not specifically called out by the Guam EPA staff, but conclude the findings in the GIS shapefiles presented in the associated figures.

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Figure 8-109. Location of Agat Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Togcha Beach at Agat Park is demonstrated through an analysis of water quality monitoring data at this site. Seasonal analysis and water quality duration analyses show that the highest concentrations are observed during the wet season (Figure 8-104) and under high flow conditions (Figure 8-106). Elevated levels during the dry season and low flow conditions may be a result from local wastewater sources. These water quality trends suggest that stormwater and wastewater sources are contributors to the bacteria levels at Togcha Beach near Agat Park. The effects of stormwater runoff on water quality are enhanced by the presence of roads, sewer mains, and dense impervious cover which are all present in the Togcha Beach drainage area. The significant number of beach advisories at Togcha Beach is likely the result of elevated bacteria levels from these sources.

TMDL Components Table 8-33 presents the TMDL for Togcha Beach - Agat Bay, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-33 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

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Table 8-33. TMDL summary (Site S-03: Agat Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

223

Instantaneous

104

9,006

281

254

290

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-34 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-34. Reductions required to meet the TMDL (Site S-03: Agat Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

71% 98%

--32%

--60%

-----

86% 99%

--72%

--55%

--24%

55% 65%

Note: --- indicates no reductions required for this condition

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8.12. Togcha Beach â&#x20AC;&#x201C; Beach at SCA (S-17) Togcha Beach near Southern Christian Academy (SCA) (RBMP site S-17) is one of three Togcha Beach sites on the west coast of Southern Guam. Located in the village of Agat, this site is marked by the Southern Christian Academy, a non-Catholic private school.

Figure 8-112. Location of Togcha Beach at SCA relative to other TMDL sites Beach advisory decisions for Togcha Beach at SCA are made based on data collected at Agat Beach. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-113, 75 percent of beach days at Togcha Beach had a beach advisory based on data provided since 2001. This frequency of beach advisories is a significant public health issue and is in line with beach advisories in Agat Bay measured at Bangi Beach (RBMP site S-04).

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Figure 8-113. Beach advisory frequency at Togcha Beach at SCA The extent of bacteria present at Togcha Beach near SCA from 2001 through 2011 is displayed in Figure 8-114as instantaneous and five-week geomean samples of enterococci data. As shown, high variability is evident throughout the record period and exceedances of instantaneous and geomean WQS were observed. The geometric mean of all individual samples is40 counts /100 mL, while the 75th and 90th percentiles are97 and 408 counts /100 mL, respectively. The rolling geomean ranges from 9 to 671 counts/100 mL (Figure 8-114).

Figure 8-114. Enterococci data analysis at Togcha Beach at SCA 159

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Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Togcha Beach at SCA (Figure 8-115) shows that maximum observed concentrations exceeded the instantaneous WQS every year. Most notably, the maximum observed concentrations in 2001, 2004, 2008, 2009, and 2011 were two orders of magnitude greater than the instantaneous WQS. Given the critically high concentrations observed, for most years of the study period 75 percent of samples on a yearly basis did not exceed the WQS. Only in years 2003, 2006, 2009, and 2011 did 25 percent of the samples exceed the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS).

Figure 8-115. Annual analysis of enterococcus data for Togcha Beach at SCA Seasonal Analysis A seasonal analysis of bacteria data for Togcha Beach near SCAfrom 2001 to 2011 is presented in Figure 8-116. As illustrated, exceedances are not exclusive to either season since maximum observed concentrations have shown to exceed the instantaneous WQS every month of the study period. Although the greatest variability in bacteria concentrations is evident in the wet-season months of July, August, and October, substantial variability is also evident, to a lesser extent, in the dry season months. Overall, the seasonal analysis does not demonstrate any stark differences between or trends among the seasons. This finding suggests that sources of bacteria are not strongly driven by seasonal influences, and therefore, continuous dry-weather sources may be contributing bacteria loadings to Togcha Beach near SCA.

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Figure 8-116. Seasonal variation at Togcha Beach at SCA Duration Curve Analysis A duration curve framework is used in Figure 8-117, Figure 8-118, and Figure 8-119 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the majority of exceedances occur under high flow conditions, while exceedances under other flow regimes are a mix of wet-season and dryseason events. As portrayed in Figure 8-118 and Figure 8-119, wet-season events resulted in the highest bacteria concentrations; however, dry season exceedances were still significant in number and present under all flow regimes. The water quality duration analysis concludes that high bacteria levels are attributed to wet-weather sources such as stormwater runoff that may occur in either the dry or wet season. The number of dry-season exceedances demonstrated in this analysis also suggests that dryweather sources such as septic systems or leaky sewer mains may be contributing to elevated bacteria levels when runoff is not an issue.

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Figure 8-117. Water quality duration analysis of Togcha Beach at SCA

Figure 8-118. Detailed water quality duration analysis of Togcha Beach at SCA

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Figure 8-119. Wet versus dry seasonal analysis for Togcha Beach at SCA Potential Sources 5 The drainage area to Togcha Beach at SCA encompasses a densely developed coastal area and undeveloped, naturally covered lands inland (Figure 8-120). The upper portions of the watershed have expansive evergreen forest cover, grassland cover, and some shrub cover. There is some high-intensity and open-space development further inland that is connected to the shoreline development via light development and roads. The coastal development near the Togcha Beach at SCA site is not exclusive to the shoreline but spans approximately 7 miles inland. The coastal development consists of multiple dwelling, commercial dwelling, and continues single-family dwelling inland (Figure 8-121). The residential zoning inland and along the coast is supported by a sewer network and road network (Figure 8-121), both of which may facilitate the transport of stormwater runoff, thereby impacting downstream water quality. Throughout the drainage area, specifically in high-density developed areas are a few non-sewered buildings that manage waste on-site (Figure 8-120 and Table 8-37). These facilities, if maintained improperly, may serve as potential wastewater sources in the area.

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Figure 8-120. Land cover and location of Togcha Beach at SCA relative to potential source areas Table 8-37. Beach specific potential source summary (Site S-17: Togcha Beach at SCA) Site ID

S-17

Source Name (notes)

Type Wastewater Stormwater

Septic systems Sewer line breaks/blockages Stormwater runoff

Note: The sources identified in this table were not specifically called out by the Guam EPA staff, but conclude the findings in the GIS shapefiles presented in the associated figures.

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Figure 8-121. Location of Togcha Beach at SCA relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Togcha Beach near SCA is demonstrated through an analysis of water quality monitoring data at this site. The lack of a strong seasonal trend suggests that bacteria sources are not exclusive to wet-weather events (Figure 8-116). The duration curve analyses suggest, however, that both wet-weather and dry-weather sources may be contributing to bacteria levels at Togcha Beach (Figure 8-118).Dry-weather exceedances, as demonstrated in the duration curve analysis, may be triggered by wet-weather events but also point to wastewater sources in the area that may be impacting water quality. These water quality trends are consistent with potential sources identified in the area including dense impervious cover, roads, sewer mains, and septic systems. In conjunction, these sources may strongly influence bacteria in stormwater runoff; however, breaks and blocks in sewer lines and faulty septic systems may contribute to bacteria levels directly and regardless of season. The significant number of beach advisories at Togcha Beach is likely the result of elevated bacteria levels from these sources. The technical analyses presented in this assessment of Togcha Beach at SCA describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-38 presents the TMDL for Togcha Beach at SCA, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-38 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-38. TMDL summary (Site S-17: Togcha Beach at SCA) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

191

Instantaneous

104

11,564

301

221

203

218

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-39 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-39. Reductions required to meet the TMDL (Site S-17: Togcha Beach at SCA) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

84% 99%

--36%

--51%

--57%

27% 35%

81% 99%

6% 80%

--51%

--19%

46% 55%

Note: --- indicates no reductions required for this condition

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8.13. Bangi Beach (S-04) Bangi Beach (RBMP site S-04) located on Bangi Point is found on the west coast of southern Guam. Bangi Beach is about a half mile south of the village of Agat, the closest populated place. Figure 8-122shows the location of Bangi Beach and an aerial view of the area.

Figure 8-122. Location of Bangi Beach relative to other TMDL sites Data collected weekly at Site S-04 are used to make beach advisory decisions for Bangi Beach. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-123, based on data provided since 2001, 79 percent of beach days at Bangi Beach had a beach advisory. This frequency of beach advisories is a significant public health issue and is consistent with the beach advisory monitoring in Agat Bay (S-03). The high beach advisory frequencies at Bangi Beach and Togcha Beach near Agat Park indicate consistent poor water quality conditions at Agat Bay.

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Figure 8-123. Beach advisory frequency at Bangi Beach The extent of bacteria present at Bangi Beach from 2001 through 2011 is presented in Figure 8-124 as instantaneous and five-week geomean samples of enterococci data. As shown, high variability was observed throughout the record period and exceedances of both instantaneous and geomean water quality standards occurred every year. The geometric mean of all individual samples was 105 counts /100 mL, while the 75th and 90th percentiles were 365 and 2,755 counts /100 mL, respectively.The high 75th and 90th percentile concentrations demonstrate the magnitude of bacteria present at Bangi Beach. The rolling geomean ranges from 9 to 6,332 counts/100 mL (Figure 8-124) which further illustrates the extent of WQS exceedances.

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Figure 8-124. Enterococci data analysis at Bangi Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Bangi Beach (Figure 8-125) illustrates that elevated bacteria concentrations have been an issue every year since 2001.Every year maximum observed concentrations have reached over two orders of magnitude of the instantaneous WQS for the exception of 2007. Furthermore, over 25 percent of samples yearly exceed the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS). The median of samples on a yearly basis were at or near 100 counts/100 mL.

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Figure 8-125. Annual analysis of enterococcus data for Bangi Beach Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. Distinct seasonal patterns seen in Figure 8-126indicate that bacteria levels are significantly elevated in the wet-season months compared to dry-season months. Significant increases in wet-season months suggest that wet-weather events influence bacteria concentrations, and therefore stormwater issues may be contributing to the bacteria at Bangi Beach. Although trumped by wet-season concentrations, dry-season concentrations are still significantly high and nearly 25 percent of samples exceed or approach the instantaneous WQS on a monthly basis. A seasonal analysis of Bangi Beach data demonstrates significantly elevated bacteria concentrations throughout both seasons with the most exceptionally high concentrations occurring during the wet-season.

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Figure 8-126. Seasonal variation at Bangi Beach Duration Curve Analysis A duration curve framework is used in Figure 8-127, Figure 8-128, and Figure 8-129 to relate bacteria concentrations to hydrologic conditions. These figures confirm a significant number ofexceedances occur under nearly all flow regimes. As shown in Figure 8-127, most exceedances occur under high flow conditions where over 75 percent of samples are greater than the instantaneous WQS.Figure 8-128 strongly suggests the influence of stormwater runoff since nearly every runoff event resulted in an exceedance and wet-event exceedances are evident in every flow regime. Although dry-season exceedances may be a result of a rainfall event, they may also be indicative of potential wastewater sources in the area. The significant number of dry-weather exceedances (Figure 8-128) and elevated dryseason concentrations (Figure 8-129) suggest that dry-weather sources, such as septic systems and leaky sewer mains, are influencing the water quality at Bangi Beach.

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Figure 8-127. Water quality duration analysis of Bangi Beach

Figure 8-128. Detailed water quality duration analysis of Bangi Beach

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Figure 8-129. Wet versus dry seasonal analysis for Bangi Beach Potential Sources 5 Finile Creek runs about 20 miles before discharging into Bangi Beach spanning developed and undeveloped land cover. The middle to lower portions of the drainage area is highly developed and is zoned for primarily single-family dwelling and light commercial and multiple dwellings (Figure 8-130and Figure 8-131). The majority of the watershed is zoned for agricultural lands and is naturally covered by evergreen forest, cultivated crop, and shrub. Some military lands are found in the far upper portions of the drainage area. Dense sewer and road networks are present throughout the lower, developed portion of the drainage area (Figure 8-131). During rainfall events, faulty sewer lines, impervious cover, and a road network can enhance the effects of stormwater runoff on the receiving waters. Other sources of bacteria have been identified in the lower portions of the drainage area to include untreated sewage discharge, illegal dumping, and a piggery (Figure 8-130). These wastewater sources have their greatest effect on water quality during dry-weather conditions, but during a rainfall the effects of these sources can be exacerbated by stormwater runoff. Other potential sources identified by Guam EPA include sewer line blocks or breaks, SSOs, and river discharge (Table 8-40).

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Figure 8-130. Land cover and location of Bangi Beach relative to potential source areas Table 8-40. Beach specific potential source summary (Site S-04: Bangi Beach) Site ID

Source Name (notes)

Type Wastewater

S-04 Other

Sewer line block/break SSO River discharge

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Figure 8-131. Location of Bangi Beachrelative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Bangi Beach is demonstrated through an analysis of water quality monitoring data at this site.Seasonal patterns, for example, show that elevated concentrations are observed year-round with exceptionally high concentrations occurring during the wet season (Figure 8-126). Duration curve analyses demonstrate significant exceedances under all flow regimes and that both wet-weather and dry-weather events are accountable for elevated concentrations (Figure 8-128). These water quality trends suggest that dry-weather sources and wet-weather sources influence the water quality at Bangi Beach. Wet-weather sources, such as stormwater runoff, are enhanced by the heavily developed area surrounding Bangi Beach and local wastewater sources. Wastewater sources identified, such as sewer line breaks and SSOs, may affect water quality during both dry- and wet-weather events; however wastewater sources such as untreated discharges and illegal dumping grounds may affect Bangi Beach most during dry weather. The technical analyses presented in this assessment of Bangi Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-41 presents the TMDL for Bangi Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-41 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-41. TMDL summary (Site S-04: Bangi Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

1,304

136

Instantaneous

104

21,162

2,501

470

259

1,111

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-42 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-42. Reductions required to meet the TMDL (Site S-04: Bangi Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

95% 99%

62% 89%

28% 83%

--47%

30% 89%

98% 100%

79% 96%

59% 77%

37% 81%

84% 94%

Note: --- indicates no reductions required for this condition

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8.14. Nimitz Beach (S-05) Nimitz Beach (RBMP site S-05) is located on the southern edge of Agat on the west coast of southern Guam. The beach is located on the shore of Taleyfac Bay and is a popular site and recreational area with several pavilions for public use. Figure 8-132shows the location of Nimitz Beach and an aerial view of the area.

Figure 8-132. Location of Nimitz Beach relative to other TMDL sites Data collected weekly at the Nimitz Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-133, Nimitz Beach has a beach advisory frequency of 51 percent based on data since 2001. This frequency of beach advisories is relatively significant but substantially better than the beach advisory frequencies in Agat Bay (75-79 percent) just north of Nimitz Beach.

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Figure 8-133. Beach advisory frequency at Nimitz Beach The extent of bacteria present at Nimitz Beach from 2001 through 2011 is presented in Figure 8-134as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards every year. The geometric mean of all individual samples was 41 counts /100 mL, while the 75th and 90th percentiles were 100 and 314 counts /100 mL, respectively.The rolling geomean ranges from 7.8 to 629 counts/100 mL (Figure 8-134) illustrating the extent of impairment observed at Nimitz Beach.

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Figure 8-134. Enterococci data analysis at Nimitz Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Nimitz Beach (Figure 8-125) illustrates that elevated bacteria concentrations have been an issue every year since 2001. Every year maximum observed concentrations have reached one or two orders of magnitude beyond the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS). In most recent years (20092011), 25 percent of samples on a yearly basis exceeded the instantaneous WQS. The 75th percentile concentrations for the remaining years were either at or near 100 counts/ 100 mL, suggesting a generally high presence of bacteria at Nimitz Beach.

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Figure 8-135. Annual analysis of enterococcus data for Nimitz Beach Seasonal Analysis A seasonal analysis on enterococcus data for Nimitz Beach is presented in Figure 8-136 to assess patterns of bacteria exceedances during dry- and wet-weather seasons. As shown, maximum observed concentrations exceeding instantaneous WQS were observed during both seasons; however, exceedances reaching two orders of magnitude beyond the WQS occurred exclusively during the wet-season. The wet season months of July through November observed the highest bacteria concentrations where 25 percent of samples exceeded the instantaneous WQS each month. Although exceedances were not as common, the dry season months demonstrated significant variability in bacteria concentrations. Overall, the seasonal analysis illustrated that significant bacteria concentrations occur during both the wet and dry seasons at Nimitz Beach with the highest concentrations occurring in the wet-season months.

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Figure 8-136. Seasonal variation at Nimitz Beach Duration Curve Analysis A duration curve framework is used in Figure 8-137, Figure 8-138 and Figure 8-139 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the highest concentrations are observed under high flow conditions and that a substantial number of exceedances occur under all flow regimes.Wet- and dry-weather events have been related to the exceedances which suggest that sources of bacteria may be mixed. For instance, the elevated wet- and dry- seasons observations under moist to dry flow conditions can be attributed to rainfall events and/or wastewater influences (Figure 8-138). Stormwater runoff can be attributed to exceedances during both the wet and dry seasons following a rainfall event. Wastewater sources such as septic systems, sewer lines, or wastewater treatment plant discharges may be influencing bacteria concentrations year-round but have the most significant impact on water quality during the dry season or dry weather.

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Figure 8-137. Water quality duration analysis of Nimitz Beach

Figure 8-138. Detailed water quality duration analysis of Nimitz Beach

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Figure 8-139. Wet versus dry seasonal analysis for Nimitz Beach Potential Sources 5 There is mixed cover in the drainage area to Nimitz Beach. Vegetated cover (i.e., evergreen forest, cultivated crop, and shrub) makes up expansive portions of the drainage area and is broken up by sparse developed areas (i.e., high-intensity and open-space) (Figure 8-140). The area immediately surrounding the Nimitz Beach site is bare land and open-space developed land and has been zoned for agricultural use (Figure 8-141). The inland drainage area is zoned for single-family dwellings and planned unit development. These zonings are greater than the current developed land cover indicating that there is room for growth. A small road network is present in the area and there is no extensive sewer line network beyond the main line that runs along the coast. The substantial developed cover along the coast does facilitate the effects of stormwater runoff. In addition, potential sources identified in Figure 8-140 that are in close proximity to Nimitz Beach include a public restroom and untreated sewage discharge. These can be considered as dryweather sources that can contribute to bacteria levels year-round. Guam EPA staff has identified other specific sources such as stormwater runoff, septic systems, and recreational activities as potential contributors to the bacteria levels in the area (Table 8-43). In Figure 8-140 and Figure 8-141, a marina can be seen within a few miles north of Nimitz Beach which can be the source of recreational activity and bacterial influences.

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Figure 8-140. Land cover and location of Nimitz Beachrelative to potential source areas Table 8-43. Beach specific potential source summary (Site S-05: Nimitz Beach) Site ID

Source Name (notes)

Type Wastewater

Septic systems

Stormwater

Stormwater runoff Marina and Recreational Boating

S-05 Recreational and Other

Boat Discharge River discharge

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Figure 8-141. Location of Nimitz Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Nimitz Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show no strong trends between seasons, but high variability is evident year-round (Figure 8-136). Water quality duration curve analyses also demonstrate wet-weather and dry-weather exceedances occurring in nearly all flow regimes. These trends indicate that wet-weather and dry-weather sources play a role in influencing bacteria levels at Nimitz Beach. Specific sources in the area that are consistent with these trends include factors contributing to stormwater runoff such as high impervious cover near the shore, a public restroom, and untreated sewage discharge in the vicinity of the beach, and a nearby marina were recreational activities may be directly affecting the water quality at Nimitz Beach. The significant number of beach advisories at Nimitz Beach is likely the result of elevated bacteria levels from these sources. The technical analyses presented in this assessment of Nimitz Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-44 presents the TMDL for Nimitz Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are

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presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-44 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-44. TMDL summary (Site S-05: Nimitz Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

203

Instantaneous

104

7,415

281

148

218

263

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-45 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-45. Reductions required to meet the TMDL (Site S-05: Nimitz Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

76% 94%

6% 50%

--30%

--52%

--13%

84% 99%

14% 65%

--27%

--47%

70% 78%

Note: --- indicates no reductions required for this condition

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8.15. Umatac Bay (S-06) Umatac Bay (RBMP site S-06) lies on the southwestern coast of Guam in the village of Umatac and is part of the Umatac watershed (Figure 8-144). The rocky shore of Umatac Bay offers a scenic walk, tables, benches, and a basketball court for visitors and recreational users. Umatac Beach, located on the eastern shore of Umatac Bay is a popular spot for many Umatac Bay visitors. Other nearby TMDL sites include Toguan Bay and Merizo Pier which are located south of Umatac Bay.

Figure 8-144. Location of Umatac Bay relative to other TMDL sites Data collected weekly at the Umatac Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-145, based on data provided since 2001, 45 percent of beach days at Umatac Beach had a beach advisory. This frequency of beach advisories is a significant public health issue, but modest compared to the next closest sites just south, Toguan Bay and Merizo Pier, where the beach advisory frequencies reach 70 percent.

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Figure 8-145. Beach advisory frequency at Umatac Bay The extent of bacteria present at Umatac Bay from 2001 through 2011 is presented in Figure 8-146 as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards every year with significant exceedances occurring in 2003 through 2005. The geometric mean of all individual samples was 39 counts /100 mL, while the 75th and 90th percentiles were 109 and 570 counts /100 mL, respectively.

Figure 8-146. Enterococci data analysis at Umatac Bay

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Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Umatac Bay is presented in Figure 8-147. The central tendency of bacteria concentrations on a yearly basis falls below the geomean WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot can be compared with the instantaneous WQS). Annual variability, however, differs year to year with maximum concentrations exceeding the instantaneous WQS every year in the study period. Notably, in recent years following 2007 the 75th percentile concentrations rose above the instantaneous WQS. Specifically, during these later years, 25 percent of samples taken were above the instantaneous WQS.

Figure 8-147. Annual analysis of enterococcus data for Umatac Bay Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. Figure 8-148 shows the seasonal variability of bacteria concentrations at Umatac Bay. Concentrations two orders of magnitude greater than the instantaneous WQS were consistently observed during the wet season. Comparatively, exceedances during the dry season were more variable and 75 percent of the dry monthly samples were below the instantaneous WQS. The consistently high concentrations observed from July through November indicate the importance of wet season sources at Umatac Bay.

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Figure 8-148. Seasonal variation at Umatac Bay Duration Curve Analysis A duration curve framework is used in Figure 8-149, Figure 8-150 and Figure 8-151 to relate bacteria concentrations to hydrologic conditions. These figures confirm that most exceedances occur under high and to a lesser extent moist flow conditions. As shown in Figure 8-149, over 75 percent of samples taken during high flow conditions were greater than the instantaneous WQS.

Figure 8-149. Water quality duration analysis of Umatac Bay 190

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Many of these exceedances, as identified in Figure 8-150, occur during wet season or stormwater runoff events. Most of the other exceedances occur during the wet season with few exceptions occurring during the dry season and under low flow conditions. In Figure 8-151, high and moist conditions both demonstrate elevated bacteria levels during wet and dry seasons. Under these flow conditions, dry season bacteria concentrations generally exceeded those during the wet season. This is expected since long antecedent periods of no rainfall causes the build-up of bacteria-bound particles to be washed-off in a dry season rainfall event. Overall, rainfall events during both wet and dry seasons influence the presence of bacteria at Umatac Bay. The significant number of exceedances occurring under high or moist flow conditions (Figure 8-149, Figure 8-150, and Figure 8-151) are indicative of periodic stormwater issues such as SSOs and seeps connected to stormwater ponds/sources.

Figure 8-150. Detailed water quality duration analysis of Umatac Bay

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Figure 8-151. Wet versus dry seasonal analysis for Umatac Bay Potential Sources 5 The drainage area to Umatac Bay consists of primarily vegetated cover including forest, grassland/herbaceous, and shrub cover (Figure 8-152). A network of Palustrine wetlands are found within the watershed, and high intensity, developed land can also be found by the outlet of the watershed, near Umatac Bay. Zoned land uses in Figure 8-153 confirm that nearly the entire watershed is protected as conserved or preserved lands. A relatively small area is zoned for multiple dwelling land use in the lower reaches of the watershed near Umatac Bay. Although the land cover only identifies limited area of high intensity development, zoned designations indicate there is room for growth. The zoning designations in Figure 8-153 coincide with the specific sources identified in Figure 8-152. Three specific sources have been identified in the drainage area including a non-sewered public restroom. This public restroom along with several other identified non-sewered buildings in the area can be potential sources of bacteria if they are poorly maintained or if leaks exist (Figure 8-152). A dense drainage network also exists near Umatac Bay, where sewer line blockages and breaks and SSOs could contribute to elevated bacteria levels. Additional potential sources identified by Guam EPA staff are presented in Table 8-48 which include stormwater runoff and river discharge. Upland non-point sources such as wildlife and stormwater runoff can reach the Umatac River can eventually flow into Umatac Bay.

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Figure 8-152. Land cover and location of Umatac Bay relative to potential source areas Table 8-48. Beach specific potential source summary (Site S-06: Umatac Bay) Site ID S-06

Type Stormwater Other

Source Name Stormwater runoff River discharge

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Figure 8-153. Location of Umatac Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Umatac Bay is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed between the wet weather months of July and November (Figure 8-148). In addition, elevated bacteria concentrations occur under high flow conditions during both wet and dry seasons. These water quality trends suggest that SSOs or sewer leaks may be contributing to elevated bacteria levels under high flow conditions and during both wet and dry seasons (Figure 8-150 and Figure 8-151). These trends are consistent with the presence of potential stormwater sources identified including a sewage drainage network near Umatac Bay and several non-sewered buildings. The relatively high number of beach advisories posted at Umatac Beach can also be attributed to these sources. The technical analyses presented in this assessment of Umatac Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-49 presents the TMDL for Umatac Bay, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-49 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-49. TMDL summary (Site S-06: Umatac Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

534

Instantaneous

104

11,199

676

238

120

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-50 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-50. Reductions required to meet the TMDL (Site S-06: Umatac Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

96% 99%

51% 92%

--56%

-----

93% 99%

30% 81%

--56%

--72%

-----

Note: --- indicates no reductions required for this condition

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8.16. Toguan Bay (S-07) Toguan Bay (RBMP site S-07) is one of three TMDL sites located on the southwestern coast of Guam (Figure 8-154). Umatac Bay and Merizo Pier are located to the north and south of Toguan Bay, respectively. Near the village of Merizo and located in the Toguan watershed, Toguan Bay is an ideal location for biologic and oceanographic study due to the presence of coral reefs in the area. Figure 8-154 shows the location of Toguan Bay and an aerial view of the area.

Figure 8-154. Location of Toguan Bay relative to other TMDL sites Data collected weekly at the Toguan Bay site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown inFigure 8-155, based on the data provided 70 percent of beach days since 2001 had a beach advisory at Toguan Bay. This exceeds the frequency of beach advisories seen at Toguan Bay; however, it about matches the number of advisories also experienced at Merizo Pier, just south of Toguan Bay.

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Figure 8-155. Beach advisory frequency at Toguan Bay Instantaneous and rolling five-week geomean samples of enterococci data collected at Toguan Bay from 2001 through 2011 is presented in Figure 8-156. Samples exceeded both instantaneous and geomean water quality standards every year with significantly high and consistent exceedances occurring in 2007 through 2011. The geometric mean of all samples collected at Toguan Bay is 108 counts /100 mL, while the 75th and 90th percentiles were 360 and 1,531 counts /100 mL, respectively. The rolling geomean ranges from 9 to 4,200 counts/100 mL (Figure 8-156).

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Figure 8-156. Instantaneous and geomean water quality data at Toguan Bay Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Toguan Bay site is presented in Figure 8-157. The central tendency of bacteria concentrations on a yearly basis fell above the instantaneous WQS for years following 2005 for except 2008 where the annual geomean fell below the instantaneous WQS. The median was also close to or above the geomean WQS throughout the entire data record (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot can be compared with the instantaneous WQS). Annual variability, however, resulted in maximum concentrations exceeding the instantaneous WQS every year of the study period. In all of these sampled years, 25 percent of samples taken were above the instantaneous WQS.

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Figure 8-157. Annual analysis for Toguan Bay Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. The seasonal variability of bacteria concentrations at Toguan Bay is presented in Figure 8-158. Concentrations two orders of magnitude greater than the instantaneous WQS were consistently observed during the wet season. Comparatively, exceedances during the dry season were more variable; 50 percent of the dry monthly samples were above the geometric mean WQS. The consistently high concentrations observed from July to December suggest the influence of wet season sources at Toguan Bay.

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Figure 8-158. Seasonal variation at Toguan Bay Duration Curve Analysis A duration curve framework is used in Figure 8-159, Figure 8-160 and Figure 8-161 to relate bacteria concentrations to hydrologic conditions. These figures demonstrate that significant exceedances occur under high and moist flow conditions and exceedances continue to be present in dry and low flow conditions. All flow regimes had at least 25 percent of exceedances of the instantaneous WQS. As shown in Figure 8-159, samples taken during high and moist flow conditions had the highest bacteria concentrations, however, a significant number of exceedances were present under other flow conditions. Many of these exceedances, as identified in Figure 8-160, occur during wet season or stormwater runoff events. However, a significant portion of exceedances were also dry weather events under mid-range to low flow conditions. In Figure 8-161, high and moist conditions both demonstrate elevated bacteria levels during wet and dry seasons; however, dry season bacteria concentrations generally exceeded those during the wet season. This is expected since long antecedent periods of no rainfall causes the build-up of bacteria-bound particles to be washed-off in a dry season rainfall event. Overall, rainfall events during both wet and dry seasons influence the presence of bacteria at Toguan Bay and exceedances occur under all flow regimes (Figure 8-159, Figure 8-160 and Figure 8-161). The exceedances under all flow regimes, particularly during dry weather and under low flow conditions, are indicative of potential point sources in the drainage area.

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Figure 8-159. Water quality duration analysis of Toguan Bay

Figure 8-160. Detailed water quality duration analysis of Toguan Bay

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Figure 8-161. Wet versus dry seasonal comparison at Toguan Bay Potential Sources The drainage area to Toguan Bay consists of primarily vegetated cover including mostly grassland/herbaceous cover, some shrub cover, and Evergreen forest cover in the headwaters (Figure 8-162). A pocket of Palustrine wetlands are found in the headwaters, while Estuarine wetlands are identified near Toguan Bay. The zoned land uses in Figure 8-163 confirm that nearly the entire watershed is protected as conserved or preserved lands with a minor portion is designated as planned unit development along the upper western edge. The land cover and zoned map figures demonstrate that the drainage area to Toguan Bay consists of primarily undeveloped lands. Specific sources identified in the drainage area include the Umatac/Merizo Sewage Treatment Plant (STP) and an untreated sewage discharge site (Figure 8-162). These sites treat the neighboring areas of the subwatershed. Specific sources identified by the Guam EPA staff are presented in Table 8-51 and include wastewater and river discharge. These point sources may be significant contributing factors to the bacteria levels in Toguan Bay.

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Figure 8-162. Land cover and location of Toguan Bay relative to potential source areas Table 8-51. Beach specific potential source summary (Site S-07: Toguan Bay) Site ID

Type Wastewater

S-07

Other

Source Name POTW (Umatac/Merizo STP) River discharge

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Figure 8-163. Location of Toguan Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Toguan Bay is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed between July and December, indicating the importance of wet season sources at Toguan Bay (Figure 8-158). Additionally, although the highest bacteria concentrations are evident during high flow conditions, bacteria exceedances also occur under low flow conditions during the dry season (Figure 8-160). Significantly high bacteria levels during the wet season as well as elevated bacteria levels under low flow conditions and during the dry season suggest that point sources identified in Figure 8-162 and Table 8-51 are influencing water quality at Toguan Bay. The significant number of beach advisories at Toguan Bay (70 percent) is likely a result of elevated bacteria levels from these sources. The technical analyses presented in this assessment of Toguan Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-52 presents the TMDL for Toguan Bay, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-52 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-52. TMDL summary (Site S-07: Toguan Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

734

204

Instantaneous

104

12,914

4,106

424

433

211

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-53 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-53. Reductions required to meet the TMDL (Site S-07: Toguan Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

99% 99%

88% 99%

32% 71%

28% 74%

10% 51%

95% 99%

81% 97%

64% 76%

56% 85%

-----

Note: --- indicates no reductions required for this condition

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8.17. Merizo Pier – Mamaon Channel (S-08) Part of the Geus watershed, Merizo Pier – Mamaon Channel (RBMP site S-08) is located near Merizo, the southernmost village in Guam. The shoreline of Merizo is not classified as rocky or sandy, but as mangrove mudflats (Guam EPA 2010). Mamaon Channel separates Cocos Lagoon from the main island of Guam and allows boat access to Merizo. The area is known for its recreational water activity, fishing, and access to Cocos Island. As illustrated in Figure 8-164, Merizo Pier – Mamaon Channel is one of the three TMDL sites located in the southwestern region of Guam.

Figure 8-164. Location of Merizo Pier - Mamaon Channel relative to other TMDL sites Data collected weekly at the Merizo Pier – Mamaon Channel site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown inFigure 8-165, based on data provided, 70 percent of beach days since 2001 had a beach advisory at the Merizo Pier site. This frequency of advisories is comparable to that of the next closest site, Toguan Bay, just north of Merizo Pier. For the southwestern region of Southern Guam, Toguan Bay and Merizo Pier hold the highest frequencies of beach advisories.

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Figure 8-165. Beach advisory frequency at Merizo Pier – Mamaon Channel Instantaneous and rolling five-week geomean samples of enterococci data collected at Merizo Pier – Mamaon Channel from 2001 through 2011 are presented in Figure 8-166. As shown, samples exceeded both instantaneous and geomean water quality standards every year with high variability. The geometric mean of all samples collected at Merizo Pier – Mamaon Channel is 63 counts /100 mL, while the 75th and 90th percentiles were 185 and 628 counts /100 mL, respectively. The rolling five-week geomean ranges from 9 to 745 counts/100 mL (Figure 8-166).

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Figure 8-166. Enterococci data analysis at Merizo Pier â&#x20AC;&#x201C; Mamaon Channel Water Quality Analysis Annual Analysis An annual analysis of enterococci data for the Merizo Pier site (Figure 8-167) shows that maximum observed concentrations exceeded the instantaneous WQS every year. Since 2006, 25 percent of the observations fell above the instantaneous WQS on an annual basis. The yearly medians were at or below the instantaneous WQS throughout the study period; however, many median values were above the geometric mean WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot can be compared with the instantaneous WQS).

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Figure 8-167. Annual analysis for Merizo Pier - Mamaon Channel site Seasonal Analysis A seasonal analysis of bacteria data for Merizo Pier â&#x20AC;&#x201C; Mamaon Channelfrom 2001 to 2011 is presented in Figure 8-168. Although exceedances are evident during both seasons, enterococci exceedances above the instantaneous WQS are more prevalent during the wet season. At least 25 percent of samples taken monthly exceed 104 counts/100 mL during the wet season months. This analysis suggests that wet season sources within the Merizo Pier area may be controlling the bacteria levels at the shore.

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Figure 8-168. Seasonal variation at Merizo Pier - Mamaon Channel Duration Curve Analysis A duration curve framework is used in Figure 8-169, Figure 8-170 and Figure 8-171 to relate bacteria concentrations to hydrologic conditions. These figures confirm exceedances mostly occur under high flow conditions. As shown in Figure 8-169, over 75 percent of samples taken during high flow conditions were greater than the instantaneous WQS. Many of these exceedances, as identified in Figure 8-170, occur during wet season or stormwater runoff events. Figure 8-170 also illustrates significant exceedances under dry and low flow conditions occurring during the dry season. As demonstrated in Figure 8-171, a significant number of exceedances occur during the wet season under nearly all flow conditions. Under high flow conditions, however, dry season bacteria concentrations are significantly high due to the washoff of build-up on land surfaces after long antecedent periods of little to no rainfall. Overall, the wet season and the rainfall events during both seasons influence the presence of bacteria at Merizo Pier â&#x20AC;&#x201C; Mamaon Channel. The significant number of exceedances occurring under high flow conditions (Figure 8-169, Figure 8-170 and Figure 8-171) are indicative of periodic stormwater issues such as SSOs and seeps connected to stormwater ponds/sources. In addition, dry-weather geometric mean exceed the WQS during all flow conditions, suggesting that continuous dry-weather sources are present.

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Figure 8-169. Water quality duration analysis of Merizo Pier - Mamaon Channel

Figure 8-170. Detailed water quality duration analysis of Merizo Pier - Mamaon Channel

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Figure 8-171. Wet versus dry season comparison for Merizo Pier - Mamaon Channel Potential Sources The land cover that makes up the drainage area to Merizo Pier â&#x20AC;&#x201C; Mamaon Channel is a mix of developed and undeveloped lands (Figure 8-172). There are vast spaces of grassland/herbaceous cover with pockets of evergreen forests. High intensity and open space development can be found along the shoreline of the watershed as well as up the center and in the headwaters. Estuarine and Palustrine wetlands are not located in the vicinity of the Merizo Pier-Mamaon Channel site, but are located on the northern and southern edges of the watershed shoreline. The zoned land uses in Figure 8-173 confirm that the shoreline is designated as one-family and multiple family dwellings and commercial use. Figure 8-173 also identifies the majority of the watershed zoned for agricultural land use. The sewer mains and roadway network shown in Figure 8-173 are also located along the shoreline and within the developed areas of the watershed. According to Guam EPA staff, sewer line breaks or blockages and SSOs have been known to occur in this drainage area (Table 8-54). Point sources illustrated in Figure 8-172 identify the Umatac/Merizo STP located along the shore north of the Merizo Pier â&#x20AC;&#x201C; Mamaon Channel site. Other specific sources of bacteria have also been identified in the drainage area including public restrooms, a stormwater runoff point, untreated sewage discharge, and improper BMPs of grease traps. In addition, nine non-sewered buildings are located along the shoreline which can pose a threat to water quality of the coastal waters if poorly maintained or leaks exist.

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Figure 8-172. Land cover and location of Merizo Pier â&#x20AC;&#x201C; Mamaon Channel relative to potential source areas Table 8-54. Beach specific potential source summary (Site S-08: Merizo Pier - Mamaon Channel). Site ID

Type

S-08

Wastewater

Source Name Sewer line block/break SSO

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Figure 8-173. Location of Merizo Pier – Mamaon Channelrelative to zoned land use Linkage Analysis The numeric target for this TMDL is Guam’s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Merizo Pier – Mamaon Channel is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during most of the wet season and some dry season months indicating that sources at Merizo Pier – Mamaon Channel are constant and may be local point sources (Figure 8-168). The connection between local point sources and exceedances is further confirmed by examining the effect of flow conditions. The flow regime analysis demonstrated high bacteria concentrations in high and moist flow conditions (Figure 8-169) but also revealed that a significant number of exceedances occurred under low flow conditions during the dry season (Figure 8-170). These indicators suggest that local point sources such as treatment plant discharges, sewer line breaks, or faulty septic systems may be potential sources of bacteria. These potential sources are consistent with the specific sources present in the drainage area such as the Umatac/Merizo STP, sewer mains and non-sewered buildings found along the coast. The significant number of beach advisories at Merizo Pier is likely the result of elevated bacteria levels associated with these sources. The technical analyses presented in this assessment of Merizo Pier - Mamaon Channel describe the relationship between water quality patterns and potential sources at this location. The loading capacity and allocations are all concentrations set at the criteria values for enterococci bacteria. This TMDL will clearly meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-55 presents the TMDL for Merizo Pier - Mamaon Channel, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-55 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-55. TMDL summary (Site S-08: Merizo Pier â&#x20AC;&#x201C; Mamaon Channel) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

333

Instantaneous

104

2,475

627

457

264

189

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-56 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-56. Reductions required to meet the TMDL (Site S-08: Merizo Pier - Mamaon Channel) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

96% 97%

57% 94%

1% 76%

9% 58%

25% 45%

89% 95%

55% 82%

33% 77%

50% 82%

-----

Note: --- indicates no reductions required for this condition

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8.18. Inarajan Pool (S-09) Two TMDL sites are located in the southeastern region of Guam, Inarajan Pool and Inarajan Bay. The southernmost site, Inarajan Pool (RBMP site S-09), is outside Inarajan Bay along the eastern shoreline of Guam and is part of the Inarajan watershed. The Inarajan Pool provides natural bathing spots since coral outcroppings serve as natural protection from the ocean currents. Figure 8-174 shows the location of Inarajan Pool and an aerial view of the area.

Figure 8-174. Location of Inarajan Pool relative to other TMDL sites Data collected weekly from the Inarajan Pool site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-175, based on available data, 40 percent of beach days since 2001 had a beach advisory at Inarajan Pool. Inarajan Bay, the only other site on the southeastern tip of Guam, had a significantly high frequency in comparison.

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Figure 8-175. Beach advisory frequency at Inarajan Pool Instantaneous and rolling five-week geomean samples of enterococci data collected at Inarajan Pool from 2001 through 2011 is presented in Figure 8-176. As shown, samples exceeded both instantaneous and geomean water quality standards every year with significantly variability. The geometric mean of all samples collected at Toguan Bay is 31 counts /100 mL, while the 75th and 90th percentiles were 52 and 327 counts /100 mL, respectively. The rolling five-week geomean ranges from 9 to 632 counts/100 mL (Figure 8-176).

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Figure 8-176. Enterococci data analysis at Inarajan Pool Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Inarajan Pool site is presented in Figure 8-177. Although the central tendency of annual bacteria concentrations fell below the instantaneous WQS every year of the study period, variability in the data resulted in exceedances of the WQS in most years and at times to the extent of two orders of magnitude. In years following 2009, 75th percentile concentrations increased and approached 100 counts/100 mL compared to earlier years of the study. The annual medians were generally below the geometric mean WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot can be compared with the instantaneous WQS).

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Figure 8-177. Annual analysis for Inarajan Pool site Seasonal Analysis The seasonal variability of bacteria concentrations at Inarajan Pool is presented in Figure 8-178. The seasonal analysis demonstrates greater monthly medians for the wet season months compared to the dry season months. 25 percent of samples taken during the wet season months of August, September, and October had enterococci concentrations greater than the instantaneous WQS. During the dry season months, 75 percent of samples taken were below the instantaneous WQS; however, variability in the data did reach over the instantaneous WQS during these months.

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Figure 8-178. Seasonal variation at Inarajan Pool Duration Curve Analysis A duration curve framework is used in Figure 8-179, Figure 8-180 and Figure 8-181 to relate bacteria concentrations to hydrologic conditions. These figures confirm that most exceedances occur under high flow conditions. As shown in Figure 8-179, the geomean of samples taken during high flow conditions is greater than the instantaneous WQS. Exceedances under high flow conditions, as identified in Figure 8-180, occur during wet season or stormwater runoff events. Most of the other exceedances also occur during the wet season or stormwater events with the exception of a subset of dry weather events. In Figure 8-181, exceedances most commonly occur during the wet season under high flow conditions. Some dry season samples are also accountable for high bacteria levels specifically under moist flow conditions. Overall, despite variability, elevated bacteria concentrations are common under high flow conditions which can be indicative of periodic stormwater issues such as SSOs and seeps connected to stormwater ponds/sources.

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Figure 8-179. Water quality duration analysis of Inarajan Pool

Figure 8-180. Detailed water quality duration analysis of Inarajan Pool

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Figure 8-181. Wet versus dry season comparison for Inarajan Pool Potential Sources The drainage area to Inarajan Pool is a mix of developed and undeveloped lands (Figure 8-182). In addition to two Palustrine wetlands, grassland/herbaceous cover, evergreen forest, and shrub cover makeup the majority of the watershed. High intensity and open space developed areas are found in the lower portions of the watershed near the Inarajan Bay and along the coastal shore. This bay area has also been zoned for mostly one-family dwellings and light commercial and multiple dwelling uses (Figure 8-183). Inland areas upstream of the bay area are zoned for agricultural land use. Several potential sources of bacteria have been identified near Inarajan Pool. For instance, public restrooms and a few non-sewered buildings (Figure 8-182) are present in addition to SSOs and stormwater runoff identified by Guam EPA staff (Table 8-57). These may all be potential sources contributing to the water quality of Inarajan Pool. Furthermore, a portion of the sewer main network is located in close proximity to the Inarajan Pool site that may contribute to elevated bacteria if maintenance is poor or leaks exist.

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Figure 8-182. Land cover and location of Inarajan Pool relative to potential source areas Table 8-57. Beach specific potential source summary (Site S-09: Inarajan Pool) Site ID S-09

Type

Source Name

Wastewater

SSO

Stormwater

Stormwater runoff

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Figure 8-183. Location of Inarajan Pool relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Inarajan Pool is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed between the wet weather months, specifically August through October (Figure 8-178). In addition, elevated bacteria concentrations occur under high flow conditions during both wet and dry seasons (Figure 8-179, Figure 8-180, and Figure 8-181). These water quality trends suggest that stormwater issues such as SSOs and stormwater runoff may be contributing to elevated bacteria levels under high flow conditions and during both wet and dry seasons. These trends are consistent with the presence of potential stormwater sources identified including a nearby sewer drainage network and stormwater runoff discharges. The technical analyses presented in this assessment of Inarajan Pool describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-58 presents the TMDL for Inarajan Pool, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses

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an implicit MOS, described above in Section 7.3. Table 8-58 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-58. TMDL summary (Site S-09: Inarajan Pool) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

206

Instantaneous

104

7,114

565

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-59 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-59. Reductions required to meet the TMDL (Site S-09: Inarajan Pool) Flow Conditions (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

7% ---

40% 90%

-----

85% 99%

11% 79%

-----

Note: --- indicates no reductions required for this condition

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8.19. Inarajan Bay (S-10) Inarajan Bay (RBMP site S-10) is part of the Inarajan watershed and is located in the southeastern region of Guam, north of Inarajan Pool. The 1.71 mile Inarajan River flows into the Inarajan Bay. Near the bay is the village of Inarajan known as the most distinctly Spanish-style village on the island that has preserved its ancient style and traditions over the decades. Figure 8-184 shows the location of Inarajan Bay and an aerial view of the area.

Figure 8-184. Location of Inarajan Bay relative to other TMDL sites Data collected weekly at the Inarajan Bay site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-185, based on data provided, 72 percent of beach days had a beach advisory at Inarajan Bay. This is high compared to the advisory frequencies occurring at the nearby Inarajan Pool site.

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Figure 8-185. Beach advisory frequency at Inarajan Bay The extent of bacteria present at Inarajan Bay from 2001 through 2011 is presented in Figure 8-186 as instantaneous and five-week geomean samples of enterococci data. Samples exceeded both instantaneous and geomean water quality standards every year with the most frequent exceedances occurring in 2003 and 2004. The geometric mean of all individual samples was 76 counts /100 mL, while the 75th and 90th percentiles were 232 and 1,278 counts /100 mL, respectively. The rolling five-week geomean concentrations range from 10 to 3,155 counts/100 mL.

Figure 8-186. Enterococci data analysis at Inarajan Bay 227

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Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Inarajan site is presented in Figure 8-187. Although observed maximum concentrations consistently fell above the instantaneous WQS, the central tendency of bacteria concentrations on a yearly basis falls below the instantaneous WQS, but frequently above the geomean WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot can be compared with the instantaneous WQS). For nearly every year of the study period, 25 percent of the annual samples fell above the instantaneous WQS for the exception of 2001 and 2006 where the 75 percentile concentrations were slightly below 104 counts/100 mL.

Figure 8-187. Annual analysis for Inarajan Bay site Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. Figure 8-188 shows the seasonal variability of bacteria concentrations at Inarajan Bay. As shown, variability and maximum observed concentrations resulted in WQS exceedances for both wet- and dry-seasons with greater monthly medians occurring in the wet season. During the wet season, more than 25 percent of all monthly samples exceeded the WQS. In addition, maximum observed concentrations exceeded the WQS by two orders of magnitude nearly every month except November. Although exceedances are not as frequent during the dry season, the maximum observed concentrations range from 1,000 counts/100 mL to over 10,000 counts/100 mL. The elevated concentrations of bacteria are evident during wet and, to a lesser extent, dry-season months.

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Figure 8-188. Seasonal variation at Inarajan Bay Duration Curve Analysis A duration curve framework is used in Figure 8-189, Figure 8-190 and Figure 8-191 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the greatest exceedances occur under high and, to a lesser extent, moist flow conditions. As shown in Figure 8-189, the percentage of samples greater than the instantaneous WQS during high flow and moist flow conditions are 75 and 50 percent, respectively. Many of these exceedances, as identified in Figure 8-190, occur during wet season or stormwater runoff events. In addition, a significant number of elevated or exceedingly high bacteria concentrations occur during the dry weather season under dry and low flow conditions. Elevated bacteria concentrations during the dry season are also confirmed in Figure 8-191 where dry season concentrations are nearly equivalent to the wet season concentrations under every flow regime. Overall, exceedances are evident under all flow regimes and during both dry and wet seasons. Although the exceedances are exceedingly high under high flow and wet-weather conditions, the number of exceedances under low flow and dry weather conditions is also significant as they are indicative of potential point sources contributing to the elevated bacteria levels.

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Figure 8-189. Water quality duration analysis of Inarajan Bay

Figure 8-190. Detailed water quality duration analysis of Inarajan Bay

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Figure 8-191. Wet versus dry season comparison for Inarajan Bay Potential Sources 5 The Inarajan River, surrounded by Palustrine wetlands, drains to Inarajan Bay as illustrated in Figure 8-192. Inland from the bay shore, land cover is mostly evergreen forest, grassland/herbaceous cover, bare, and shrub. The area immediately surrounding the bay is densely populated and zoned for single and multiple family dwellings (Figure 8-193). Also demonstrated in Figure 8-193 is a dense sewer line network adjacent to the Inarajan Bay data sampling site. Water quality of the bay is primarily influenced by the immediately surrounding area and drainage received from the Inarajan River. In addition to the sewer line network, several potential sources have been identified near the Inarajan Bay area. As illustrated in Figure 8-192, untreated sewage discharge, public restrooms, and a leaching septic tank can be found along the coast of Inarajan Bay and near the sampling site. Guam EPA staff has also identified SSOs, stormwater runoff, wildlife, and river discharge as potential sources affecting Inarajan Bay (Table 8-60).

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Figure 8-192. Land cover and location of Inarajan Bay relative to potential source areas Table 8-60. Beach specific potential source summary (Site S-10: Inarajan Bay) Site ID

Type

Source Name

Wastewater

SSO

Stormwater

Stormwater runoff

S-10

Wildlife Other River discharge

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Figure 8-193. Location of Inarajan Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Inarajan Bay is demonstrated through an analysis of water quality monitoring data at this site. A seasonal analysis demonstrated that the elevated concentrations are observed during both dry and wet season months, with the consistently high concentrations occurring through the entire wet season (Figure 8-188). In addition, elevated bacteria concentrations occur under high and moist flow conditions during both wet and dry seasons (Figure 8-189, Figure 8-190, and Figure 8-191). These water quality trends suggest that stormwater issues such as SSOs and stormwater runoff may be contributing to elevated bacteria levels under high flow conditions and during both wet and dry seasons. These trends are consistent with the presence of potential stormwater sources identified including a nearby sewer drainage network and stormwater runoff discharges. Specific sources such as the leaching septic tank near the sampling site and untreated sewage discharge may also be contributing to the elevated bacteria concentrations observed during the dry season. The significant number of beach advisories at Inarajan Bay is likely the result of elevated bacteria levels from these sources. The technical analyses presented in this assessment of Inarajan Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-61 presents the TMDL for Inarajan Bay, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit Margin of Safety (MOS), described above in Section 7.3. Table 8-61 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-61. TMDL summary (Site S-10: Inarajan Bay). Concentration by Duration Curve Zone (count/100 mL)

Measurement Type

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Instantaneous

104

14,694

1,467

237

111

Geomean

1,203

130

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-59 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) tothe TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-62. Reductions required to meet the TMDL (Site S-10: Inarajan Bay) Needed Reductions Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Conditions (reductions expressed as percentage) High

Moist

Mid

Dry

Low

93% 99%

70% 87%

27% 30%

--51%

--6%

97% 99%

74% 94%

30% 64%

7% 58%

-----

Note: --- indicates no reductions required for this condition

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8.20. Talofofo Bay (S-11) Talofofo Bay (RBMP site S-11) is located in the Talofofo watershed along the eastern coast of Guam. The bay is bordered on both sides by cliffs, and a beach with dark-brown sand is situated at the end of the bay. Talofofo Bay beach serves as a popular surfing spot for locals and visitors. In addition to the surf, a sunken Japanese vessel is a popular diving spot inviting many divers and recreational users to the area. Figure 8-194 shows the location of Talofofo Bay and an aerial view of the area.

Figure 8-194. Location of Talofofo Bay relative to other TMDL sites Data collected weekly at the Talofofo Bay site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-194, 79 percent of beach days from 2007 through 2011(based on available data)had a beach advisory at the head of Talofofo Bay. The frequency of advisories at Talofofo Bay trumps the number of advisories seen at First Beach (S-18), which is within the vicinity of Talofofo Bay and has a beach advisory frequency between 10 and 20 percent.

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Figure 8-195. Beach advisory frequency at Talofofo Bay The extent of bacteria present at Talofofo Bay from 2001 through 2011 is presented in Figure 8-196. Enterococci data analysis at Talofofo Bay as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards every year with variability. The geometric mean of all individual samples was 174 counts /100 mL, while the 75th and 90th percentiles were 534 and 2,736 counts /100 mL, respectively. The range of the 5-week rolling geomean is 12 to 3,498 counts/100 mL.

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Figure 8-196. Enterococci data analysis at Talofofo Bay Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Talofofo Bay site is presented in Figure 8-197. Every year of the study period except 2005, the central tendency of bacteria concentrations fell above the instantaneous WQS. In addition, for most years, 75 percent of annual samples exceeded the geomean WQS of 35 counts/100 mL. The annual analysis of water quality at Talofofo Bay reveals that enterococci concentrations at this site are significantly high and require critical attention.

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Figure 8-197. Annual analysis for Talofofo Bay site Seasonal Analysis Seasonal variability of bacteria concentrations at Talofofo Bay is shown in Figure 8-198. As illustrated, significant water quality exceedances occur every month during the wet season with about 75 percent of monthly samples exceeding the instantaneous WQS of 104 counts/100 mL. Although dry season monthly samples are not as high as those observed during the wet season, about one-fourth of these samples exceed the instantaneous WQS on a monthly basis. The seasonal analysis reveals that elevated bacteria concentrations occur during the dry season and, to a greater extent, wet season.

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Figure 8-198. Seasonal variation at Talofofo Bay Duration Curve Analysis A duration curve framework is used in Figure 8-199, Figure 8-200 and Figure 8-201 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the greatest exceedances occur under high, moist, and mid-range flow conditions. As shown in Figure 8-199, the percentage of samples greater than the instantaneous WQS during moist and mid-range flow conditions are 75 and 50 percent, respectively. Nearly every sample observed during high flow conditions exceeds the instantaneous WQS. The majority of these exceedances, as identified in Figure 8-200, occur during wet season or stormwater runoff events. A limited number of observed exceedances occur during the dry weather season under low flow conditions. Elevated bacteria concentrations during higher flow conditions are also confirmed in Figure 8-201. In this figure, dry season concentrations are nearly equivalent to the wet season concentrations. Overall, exceedances are evident under the high, moist, and mid-range flow conditions and during both dry and wet seasons.

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Figure 8-199. Water quality duration analysis of Talofofo Bay

Figure 8-200. Detailed water quality duration analysis of Talofofo Bay

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Figure 8-201. Wet versus dry season comparison for Talofofo Bay Potential Sources 5 The drainage area to Talofofo Bay is a mostly undeveloped land with some development on the northeastern portion of the watershed (Figure 8-202). Evergreen forest cover, which contains wildlife, can be found throughout the drainage area and surrounding Talofofo Bay. A river discharges to the bay and is surrounded by Palustrine wetlands (Figure 8-202 and Table 8-63). Unlike other popular beach destinations, however, high intensity and open space development are not found along the coast but further inland (Figure 8-202 and Figure 8-203). This developed area has a significant number of nonsewered buildings as well as an untreated sewage pumping station and leaking septic tanks (Table 8-63). Near the bay are public restrooms, agricultural sites, and some light development, as illustrated in Figure 8-202. Much of the watershed is zoned for agricultural use (Figure 8-203). Although not a specific source of bacteria, the limestone geology found along the eastern regions of Southern Guam can enhance the transport of bacteria (illustrated in Section 5 maps). The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions.

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Figure 8-202. Land cover and location of Talofofo Bay relative to potential source areas Table 8-63. Beach specific potential source summary (Site S-11: Talofofo Bay) Site ID

Type Wastewater

S-11

Source Name Septic systems SSO Wildlife

Other River discharge

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Figure 8-203. Location of Talofofo Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Talofofo Bay is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the elevated concentrations occur during both the dry season and wet seasons with highest concentrations occurring in the latter (Figure 8-198). Furthermore, exceedances occur nearly under all flow regimes during both seasons (Figure 8-200 and Figure 8-201). These water quality trends suggest that a combination of point sources and stormwater issues may be contributing to elevated bacteria levels. The pumping station, septic tanks, high density sewer line network, and non-sewered buildings inland from the bay are specific sources in the area that may be affecting the water quality at the bay and linked to the 80 percent of days with beach advisories. The technical analyses presented in this assessment of Talofofo Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-64 presents the TMDL for Talofofo Bay, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses

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an implicit MOS, described above in Section 7.3. Table 8-49 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-64. TMDL summary (Site S-11: Talofofo Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

2,052

418

123

Instantaneous

104

9,896

3,451

731

227

253

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-65 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-65. Reductions required to meet the TMDL targets (Site S-11: Talofofo Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Conditions (reductions expressed as percentage) High

Moist

Mid

Dry

Low

99% 99%

91% 98%

66% 75%

2% 42%

13% 59%

98% 99%

92% 97%

79% 88%

48% 66%

-----

Note: --- indicates no reductions required for this condition

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8.21. First Beach - Talofofo (S-18) First Beach (RBMP site S-18) is located north of Talofofo Bay along the eastern coast of Guam. First Beach and Talofofo Bay are part of the Talofofo watershed. The closest city to First Beach, Ypan, is 0.40 miles from the beach. Figure 8-204 shows the location of First beach and an aerial view of the area.

Figure 8-204. Location of First Beach - Talofofo relative to other TMDL sites Data collected weekly at the First Beach - Talofofo site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-205, based on data provided, 14 percent of beach days had a beach advisory at First Beach. Compared to other sites located in the southern most region of South Guam, beach advisories are less common at First Beach. For example, at the head of Talofofo Bay, beach advisory frequencies reach nearly 80 percent of beach days.

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Figure 8-205. Beach advisory frequency at First Beach â&#x20AC;&#x201C; Talofofo The extent of bacteria present at First Beach from 2001 through 2011 is presented in Figure 8-206 as instantaneous and five-week geomean samples of enterococci data. As shown, variability in samples resulted in both instantaneous and geomean water quality exceedances with more frequent exceedances occurring since 2010. The geometric mean of all individual samples was 14 counts /100 mL, while the 75th and 90th percentiles were 10 and 52 counts /100 mL, respectively. The rolling 5-week geomeans range from 9 to 82 counts/100 mL.

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Figure 8-206. Enterococci data analysis at First Beach â&#x20AC;&#x201C; Talofofo Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the First Beach - Talofofo site is presented in Figure 8-207. The central tendency of bacteria concentrations on a yearly basis falls below both WQSs. Annual variability, however, differs year to year with maximum observed concentrations exceeding the instantaneous WQS nearly every year in the study period. The greatest variability in concentrations have been observed in more recent years, 2010 and 2011, suggesting that bacterial concentrations are on the rise at the First Beach site.

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Figure 8-207. Annual analysis for First Beach - Talofofo site Seasonal Analysis The seasonal variability of bacteria concentrations at First Beach is illustrated in Figure 8-208. The greatest concentrations and variability in bacteria concentrations occurs during the wet season months. To a lesser extent, variability also occurs during the dry months with occasional exceedances; however, the majority of dry-weather samples are below the WQSs. The variability during the wet season compared to that of the dry season suggests that stormwater issues may be contributing to bacteria concentrations observed at First Beach.

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Figure 8-208. Seasonal variation at First Beach - Talofofo Duration Curve Analysis A duration curve framework is used in Figure 8-209, Figure 8-210 and Figure 8-211 to relate bacteria concentrations to hydrologic conditions. These figures confirm that highest concentrations occur under high and moist flow conditions. The greatest variability in bacteria concentrations occurs under high flow conditions (Figure 8-209), but exceedances are still evident under both high flow and moist flow conditions (very few exceedances also occur in the mid-range and dry conditions) (Figure 8-210). From a seasonal standpoint, elevated concentrations occur during both wet and dry seasons (Figure 8-211). Overall, most of the elevated concentrations observed were either a wet season event, stormwater runoff event, or both. This suggests that the presence of bacteria may be influenced by stormwater issues such as surface runoff or storm drain overflows during or after rainfall events.

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Figure 8-209. Water quality duration analysis of First Beach (Ipan Point Beach)

Figure 8-210. Detailed water quality duration analysis of First Beach (Ipan Point Beach)

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Figure 8-211. Wet versus dry seasonal analysis for First Beach (Ipan Point Beach) Potential Sources 5 First Beach receives drainage primarily from a coastal watershed. As illustrated in Figure 8-212, the drainage area is mostly covered by evergreen forest with some residential development in center of the watershed and in close proximity to the shore. The community is serviced by on-site sewage treatment as demonstrated by the non-sewered building markers in Figure 8-212. There are no sewer mains near First Beach as shown in Figure 8-213. The area immediately surrounding this site is zoned for agriculture (Figure 8-213). Table 8-66 provides a summary of potential bacteria sources that may be contributing to the water quality observed at First Beach. Although not a specific source of bacteria, the limestone geology found along the eastern regions of Southern Guam (illustrated in Section 5 maps) can enhance the transport of bacteria. The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions.

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Figure 8-212. Land cover and location of First Beach - Talofofo relative to potential source areas Table 8-66. Beach specific potential source summary (Site S-18: First Beach - Talofofo) Site ID S-18

Type

Source Name

Stormwater

Surface runoff

Wastewater

Proximity to leaching septic tank

Note: The sources identified in this table were not specifically called out by the Guam EPA staff, but conclude the findings in the GIS shapefiles presented in the associated figures.

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Figure 8-213. Location of First Beach - Talofofo relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at First Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during the wet season. In addition, elevated bacteria concentrations occur under high flow and moist conditions during both wet and dry seasons. The water quality analysis also strongly indicates that exceedances are not frequent since the geomeans of all flow regimes and seasons fell below the WQS. These water quality trends suggest that stormwater issues, such as stormwater runoff, may be contributing to elevated bacteria levels especially during or after rainfall events. The low geomeans presented in the water quality data may be attributed to the limited number of identified potential sources. The technical analyses presented in this assessment of First Beach â&#x20AC;&#x201C; Talofofo describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-67 presents the TMDL for First Beach - Talofofo, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses

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Table 8-67. TMDL summary (Site S-18: First Beach - Talofofo) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

671

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-68 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-68. Reductions required to meet the TMDL (Site S-18: First Beach - Talofofo) Flow Conditions (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

2% ---

--15%

-----

14% 85%

-----

Note: --- indicates no reductions required for this condition

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8.22. Ipan Beach (S-12) North of First Beach along the eastern coast of Guam is Ipan Beach (RBMP site S-12). Although located near the village of Talofofo, a rural beachside community, Ipan Beach is part of the Togcha watershed and is near Mana Bay. Ipan Beach is a popular location for swimming, snorkeling, kayaking, and fishing. Ipan is also the site of the Pangelinan Quarry which provides high quality limestone aggregate. Figure 8-214 shows the location of Ipan Beach and an aerial view of the area.

Figure 8-214. Location of Ipan Beach relative to other TMDL sites Data collected weekly at the Ipan Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-215, beach advisories at Ipan beach are infrequent as only 4 percent of days had beach advisories based on available data from 2001. This is the lowest of beach advisory frequencies compared to other beaches located on the eastern coastline of Southern Guam.

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Figure 8-215. Beach advisory frequency at Ipan Beach The extent of bacteria present at Ipan Beach from 2001 through 2011 is presented in Figure 8-216 as instantaneous and five-week geomean samples of enterococci data. As shown, variability exists for both instantaneous and geomean samples every year with the most exceedances occurring in 2001 through 2004. The geometric mean of all individual samples was 13 counts /100 mL, while the 75th and 90th percentiles were 10 and 31 counts /100 mL, respectively. The rolling five-week geomean ranges from 9 to 115 counts/100 mL.

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Figure 8-216. Enterococci data analysis at Ipan Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for the Ipan Beach site is presented in Figure 8-217. As shown, bacteria concentrations observed at the site are significantly lower than other southern Guam sites. The annual central tendency of bacteria concentrations fall below both WQSs. Annual variability, however, differs year to year with maximum concentrations often exceeding the instantaneous WQS.

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Figure 8-217. Annual analysis for Ipan Beach site Seasonal Analysis Seasonal variability of bacteria concentrations at Ipan Beach is shown in Figure 8-218. Although higher bacteria concentrations occur during the wet season, variability in both seasons is evident resulting in some exceedances of the instantaneous WQS year-round.

Figure 8-218. Seasonal variation at Ipan Beach

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Duration Curve Analysis A duration curve framework is used in Figure 8-219, Figure 8-220 and Figure 8-221 to relate bacteria concentrations to hydrologic conditions. These figures confirm that the highest concentrations occur under high flow conditions. As shown in Figure 8-219, 25 percent of samples taken during high flow conditions were greater than the geometric mean WQS. Most elevated concentrations were observed during wet season or stormwater runoff events with a few occurrences during the dry season (Figure 8-220). The concern over high bacteria concentrations is confirmed to occur under high flow conditions and during both seasons as shown in Figure 8-221. High flow exceedances during the dry season are expected since long antecedent periods of no rainfall causes the build-up of bacteria-bound particles to be washed-off in a dry season rainfall event. Overall, high flow conditions during both wet and dry seasons influence the presence of bacteria at Ipan Beach, which is indicative of periodic stormwater issues such as SSOs and seeps connected to stormwater ponds/sources.

Figure 8-219. Water quality duration analysis of Ipan Beach

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Figure 8-220. Detailed water quality analysis of Ipan Beach

Figure 8-221. Wet versus dry season analysis for Ipan Beach Potential Sources 5

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Ipan Beach receives drainage from a coastal watershed. As illustrated in Figure 8-222 and Figure 8-223, the drainage area is a mix of developed and undeveloped areas with residential development in close proximity to the shore. The area is zoned for agricultural, planned unit development, and single family dwelling uses (Figure 8-222), suggesting that additional development is possible. Since there is no sewer drainage network, the community is serviced by on-site sewage treatment as shown by the non-sewered building markers in Figure 8-222. These septic systems, as identified by Guam EPA staff (Table 8-69), are a potential source of bacteria to the coastal waters. The effect of this source is enhanced by the dense road network that serves as a pathway to the coast during rainfall events. The transportation of bacteria may be further enhanced by the presence of limestone geology (illustrated in Section 5 maps) found along the eastern regions of Southern Guam. The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions.

Figure 8-222. Land cover and location of Ipan Beach relative to potential source areas Table 8-69. Beach specific potential source summary (Site S-12: Ipan Beach) Site ID

Type

S-12

Wastewater

Source Name Septic Systems

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Figure 8-223. Location of Ipan Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts/100 mL and an instantaneous maximum of 104 counts/100 mL). The relationship between this target and potential sources at Ipan Beach is demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during the wet season with some variability evident during both seasons (Figure 8-218). Elevated bacteria concentrations occur under high flow conditions during both wet and dry seasons are further confirmed in Figure 8-220 and Figure 8-221. These water quality trends suggest that stormwater runoff-related issues such as SSOs or sewer leaks may be contributing to elevated bacteria levels under high flow conditions and during both wet and dry seasons. These trends are consistent with the presence of non-sewered buildings present near Ipan Beach. The technical analyses presented in this assessment of Ipan Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-70 presents the TMDL for Ipan Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-49 also shows the observed concentrations

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associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-70. TMDL summary (Site S-12: Ipan Beach) Measurement Type

TMDL (count/ 100 mL)

Geomean

Instantaneous

104

162

Note:

Concentration by Duration Curve Zone (count/100 mL)

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-71 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) tothe TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-71. Reductions required to meet the TMDL (Site S-12: Ipan Beach) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Conditions (reductions expressed as percentage) High

Moist

Mid

Dry

Low

--23%

-----

--27%

-----

Note: --- indicates no reductions required for this condition

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8.23. Togcha Bay - Talofofo (S-13) Togcha Bay – Talofofo (RBMP site S-13) is located just north of Togcha River on the eastern coast of Guam. The beach is located near the village of Yona and is part of the Togcha watershed. Togcha Bay is a popular spot used frequently for wind surfing. Figure 8-224 shows the location of Togcha Bay –Talofofo and an aerial view of the area.

Figure 8-224. Location of Togcha Bay - Talofofo relative to other TMDL sites Data collected weekly at the Togcha Bay – Talofofo site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). From 2007 to 2011, 27 percent of beach days at Togcha Bay – Talofofo had beach advisories based on available data and as shown in Figure 8-225. The frequency of advisories at Togcha Bay is in a similar range to that of other sites also located on the eastern coastline of South Guam (Figure 8-225).

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Figure 8-225. Beach advisory frequency at Togcha Bay - Talofofo The extent of bacteria present at Togcha Bay from 2001 through 2011 is presented in Figure 8-226 as instantaneous and five-week geomean samples of enterococci data. As shown, variability exists for both instantaneous and geomean samples every year. The geometric mean of all samples at this beach from 2001 to 2011 is 25 counts/100 mL. The rolling geometric mean ranges from 9 to 1,538 counts/100 mL (Figure 8-226). While concentrations are lower at this beach than other South Guam sites, this beach is still impaired and water quality improvements are desired.

265

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Figure 8-226. Enterococci data analysis at Togcha Bay - Talofofo Water Quality Analysis Annual Analysis An annual analysis of enterococci data for the Togcha Bay â&#x20AC;&#x201C; Talofofo beach show that only in 2002 did the 75th percentile of data exceed the instantaneous WQS (Figure 8-227). Many samples taken at this beach were below detection causing the median of most years sampling to lie below 10 counts/100 mL. During three out of the past five years, 25 percent of samples taken were above the geometric mean WQS (2007, 2008, and 2011). Maximum observed concentrations exceed the instantaneous WQS every year of the study period.

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Figure 8-227. Annual enterococcus data analysis for Togcha Bay - Talofofo site Seasonal Analysis A seasonal analysis of bacteria data for the Togcha Beach site from 2001 to 2011 is presented in Figure 8-228. During the dry season, bacteria concentrations are generally low and fall below 35 counts/100 mL. Maximum observed concentrations occasionally exceed the instantaneous WQS. Comparatively, exceedances during the wet season are more frequent. As illustrated in Figure 8-228, 75 percent of the monthly samples of July, August, September and October fall above the instantaneous WQS. Wet season exceedances peak in August when the median of samples is 43 counts/100 mL and the 75th percentile of samples is 435 counts/100 mL. This analysis indicates that wet weather sources such as stormwater discharges, overflows, and runoff may be affecting the water quality at Togcha Bay.

267

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Figure 8-228. Seasonal variation at Togcha Bay - Talofofo Duration Curve Analysis Using a duration curve framework, Figure 8-229, Figure 8-230 and Figure 8-231 relate bacteria concentrations to hydrologic conditions. The highest bacteria concentrations and most exceedances at Togcha Bay occur under high flow conditions (Figure 8-229). Figure 8-230 indicates that the majority of WQS exceedances occur during the wet season and that many occur during runoff events. In a seasonal comparison, variability in bacteria concentrations can be seen for both seasons under all flow regimes (Figure 8-231). The greatest number of exceedances, however, occurs during the wet season under high flow conditions. Overall, elevated bacteria concentrations observed in Togcha bay occur during wet season events and under high flow conditions.

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Figure 8-229. Water quality duration analysis of Togcha Bay - Talofofo

Figure 8-230. Detailed water quality duration analysis of Togcha Bay â&#x20AC;&#x201C; Talofofo Beach

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Figure 8-231. Wet versus dry seasonal analysis of Togcha Bay â&#x20AC;&#x201C; Talofofo Beach Potential Sources The Togcha River subwatershed is mostly evergreen forest and cultivated crops (Figure 8-232). It is zoned for agriculture, family dwelling, and planned unit development (Figure 8-233). There are a number of non-sewered buildings surrounding the village of Talofofo. The transport of bacteria from these septic tanks can be enhanced by the presence of limestone geology found along the eastern regions of Southern Guam (illustrated in Section 5 maps). The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions. Several sources of bacteria have been identified near Togcha Bay. The Baza Gardens WWTP drains to the Togcha River and there are known SSOs to the Togcha Bay watershed. In addition, there is a golf course draining to the Togcha Bay watershed as displayed in Figure 8-232 and Table 8-72. Wildlife and discharge from the Togcha River also contribute to the bacteria load in Togcha Bay. Guam EPA staff has identified untreated sewage discharge and stormwater runoff as specific sources within the Togcha River subwatershed (Figure 8-232).

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Figure 8-232. Land cover and location of Togcha Bay - Talofofo relative to potential source areas Table 8-72. Beach specific potential source summary (Site S-13: Togcha Bay - Talofofo) Site ID

Type Wastewater

Source Name SSO POTW (Baza Gardens STP) Golf course

S-13

Wildlife Other

River discharge Nutrient loading

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Figure 8-233. Location of Togcha Bay - Talofofo relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts/100 mL and an instantaneous maximum of 104 counts/100 mL). The relationship between this target and potential sources at Togcha Bayis demonstrated through an analysis of water quality monitoring data at this site. Seasonal patterns, for example, show that the highest concentrations are observed during the wet season (Figure 8-228). Elevated bacteria concentrations occurring under high flow conditions during the wet season are also confirmed in Figure 8-230 and Figure 8-231. These trends are consistent with the presence such as wildlife, river discharge and stormwater runoff identified as sources present near Togcha Bay. Additionally, the identified sources such as septic tanks and untreated sewage discharge may be contributing to elevated bacteria levels during the dry season. The technical analyses presented in this assessment of Togcha Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

TMDL Components Table 8-73 presents the TMDL for Ipan Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are 272

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presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-49 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-73. TMDL summary (Site S-13: Togcha Bay - Talofofo) Concentration by Duration Curve Zone (count/100 mL)

Measurement Type

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

191

Instantaneous

104

14,694

387

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-74 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-74. Reductions required to meet the TMDL (Site S-13: Togcha Bay - Talofofo) Flow Conditions (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

7% ---

-----

84% 99%

--76%

--37%

-----

Note: --- indicates no reductions required for this condition

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8.24. Tagachang Beach (S-14) Tagachang Beach (RBMP site S-14) is on the east coast of southern Guam to the south of Pago Bay. In the village of Yona, Tagachang Beach Park is on an isolated beach cove surrounded by rising cliffs on all sides. A park located at the beach has several pavilions, picnic tables, and restrooms available for public use. Figure 8-234shows the location of Tagachang Beach and an aerial view of the area.

Figure 8-234. Location of Tagachang Beach relative to other TMDL sites Data collected weekly at the Tagachang Beach site are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-235, beach advisories at Tagachang Beach are minor compared to other regional beaches at 9 percent based on data from 2001.

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Figure 8-235. Beach advisory frequency at Tagachang Beach Bacteria concentrations observed at Tagachang Beach from 2001 through 2011 are presented in Figure 8-236as instantaneous and five-week geomean samples of enterococci data. As shown, instantaneous WQS exceedances occurred nearly every year; whereas, geomean WQS exceedances occurred less frequently. The highest concentrations observed occurred in 2002, 2003 and 2010. The geometric mean of all individual samples was 14 counts /100 mL, while the 75th and 90th percentiles were 10 and 43 counts /100 mL, respectively.These percentiles suggest that less than 25 percent of all samples of the study period exceeded the instantaneous WQS. The rolling geomean ranges from 9 to 63 counts/100 mL (Figure 8-236).

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Figure 8-236. Enterococci data analysis at Tagachang Beach Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Tagachang Beach from 2001 through 2011 (Figure 8-237) illustrates that bacteria concentrations generally ranged well below WQS. In recent years (2010-2011), however, the variability in bacteria concentrations grew, as shown in Figure 8-237. Despite low central tendencies, maximum observed concentrations occasionally fell above the instantaneous WQS throughout the period of record (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS).

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Figure 8-237. Annual analysis of enterococcus data for Tagachang Beach Seasonal Analysis Seasonal variability of enterococci data at Tagachang Beach demonstrates no seasonal trends (Figure 8-238). Although minor in magnitude, exceedances at Tagachang Beach occur year-round and variability remains generally constant with the exception of a few months (April, July, and August) where increasing bacteria ranges are evident. The lack of seasonal trends strongly suggests that there is no strong stormwater or wet-weather influence on the water quality at Tagachang Beach. It is possible that a local wastewater source may be present which is contributing to the infrequent, elevated bacteria levels.

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Figure 8-238. Seasonal variation at Tagachang Beach Duration Curve Analysis Similar to the seasonal analysis, a duration curve analysis did not demonstrate any strong water quality trends relative to flow conditions. Although minor in number, exceedances and elevated bacteria observations were evident in all flow regimes (Figure 8-239, Figure 8-240, and Figure 8-241). Most clearly illustrated in Figure 8-240, observed exceedances occur during runoff events, wet-season events, and dry-season events.This mix of conditions does not suggest a strong influence from a particular source type; local wastewater sources and occasional runoff may be equally contributing to the water quality conditions at Tagachang Beach.

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Figure 8-239. Water quality duration analysis of Tagachang Beach

Figure 8-240. Detailed water quality duration analysis of Tagachang Beach

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Figure 8-241. Wet versus dry seasonal analysis for Tagachang Beach Potential Sources 5 Tagachang Beach is an isolated beach on the western coast of Southern Guam. It is surrounded by vegetated cover that runs from the coast to about 5 to 10 miles inland and a narrow strip of shrub cover runs along the vegetated coastline (Figure 8-242). This vegetated cover surrounding Tagachang Beach is zoned for agricultural use (Figure 8-243). About 5 miles inland, zoning for single-family dwellings begins, which consists of open-space and high intensity developed land cover. There is an extensive road network and a dense sewer network in the northeasterly direction from Tagachang Beach (Figure 8-243). A singular road runs to the Tagachang Beach which comprises the majority of impervious cover at the site.There is a non-sewered public restroom, which may serve as a potential wastewater source identified by Guam EPA staff (Table 8-75). Although not a specific source of bacteria, the limestone geology found along the eastern regions of Southern Guam can enhance the transport of bacteria (illustrated in Section 5 maps). The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions.

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Figure 8-242. Land cover and location of Tagachang Beach relative to potential source areas Table 8-75. Beach specific potential source summary (Site S-14: Tagachang Beach) Site ID

Type

S-14

Wastewater

Source Name (notes) Septic systems

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Figure 8-243. Location of Tagachang Beach relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Tagachang Beach is demonstrated through an analysis of water quality monitoring data at this site. Water quality analysis at Tagachang Beach demonstrated limited seasonal variability and no correlation between exceedances and flow conditions. Examination of a detailed water quality duration curve indicates that a mix of runoff events, wet-season events, and dry-season events contributed to the elevated and sometimes exceedingly high bacteria concentrations. These analytical results coincide with the lack of developed land and potential sources near Tagachang Beach. Strong stormwater sources are 10 miles inland in the developed areas and are buffered by the expansive evergreen forest between the residential area and Tagachang Beach. Surrounded by vegetated, agriculturalland, the only potential source of bacteria is a non-sewered public restroom. This wastewater source likely contributes to the elevated bacteria levels at Tagachang Beach during dry-weather, and its contribution may be accelerated during wet-weather events. The technical analyses presented in this assessment of Tagachang Beach describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

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TMDL Components Table 8-76 presents the TMDL for Tagachang Beach, identifying the loading capacity expressed as concentration-based values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-76also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-76. TMDL summary (Site S-14: Tagachang Beach) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

Instantaneous

104

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-77 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-77. Reductions required to meet the TMDL (Site S-14: Tagachang Beach) Flow Condition (reductions expressed as percentage)

Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

High

Moist

Mid

Dry

Low

-----

--77%

Note: --- indicates no reductions required for this condition

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Twenty Five Guam Beaches

8.25. Pago Bay (S-15) Pago Bay (RBMP site S-15) is the most northern site on the east coast of southern Guam. It is a popular dive site and the location of the University of Guamâ&#x20AC;&#x2122;s Marine Laboratory. Figure 8-244shows the location of Pago Bay and an aerial view of the area.

Figure 8-244. Location of Pago Bay relative to other TMDL sites Data collected weekly at Pago Bay are used to make beach advisory decisions. Guam EPA issues swimming advisories based upon either an instantaneous concentration of 104 MPN/100 mL or a geometric mean concentration of 35 MPN/100 mL, over a five week period (consistent with the WQS for M-2 waters). As shown in Figure 8-245, based on data provided since 2001, 32 percent of beach days at Pago Bay had a beach advisory.

284

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-245. Beach advisory frequency at Pago Bay The extent of bacteria present at Pago Bay from 2001 through 2011 is presented in Figure 8-246as instantaneous and five-week geomean samples of enterococci data. As shown, samples exceeded both instantaneous and geomean water quality standards nearly every year with some rolling geomean concentrations reaching over 100 counts/ 100 mL. The geometric mean of all individual samples was 27 counts /100 mL, while the 75th and 90th percentiles were 51 and 288 counts /100 mL, respectively.The rolling geomean ranges from 9 to 472 counts/100 mL (Figure 8-246).

285

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-246. Enterococci data analysis at Pago Bay Water Quality Data Analyses Annual Analysis An annual analysis of enterococci data for Pago Bay from 2001 through 2011 is presented in Figure 8-247. As shown, maximum observed concentrations exceeded the instantaneous WQS every year; however, central tendencies generally fell below the WQS. In 2011, the greatest variability in bacteria concentrations was recorded where about 25 percent of the samples fell above the instantaneous WQS (note: the medians shown in this figure cannot be directly compared to the geomean WQS because they are different statistics; however, the boxplot data can be compared with the instantaneous WQS).

286

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-247. Annual analysis of enterococcus data for Pago Bay Seasonal Analysis A seasonal analysis is useful in evaluating patterns of bacteria exceedances during dry- and wet-weather seasons. In Figure 8-248, a growing trend of elevated bacteria levels in the wet-season months is evident in Pago Bay. Wet-seasons months of July, August, September, and October demonstrated the highest variability of bacteria concentrations. Variability and increased concentrations is also evident during the dry-season months; however, these concentrations generally do not exceed the instantaneous WQS. The seasonal trends suggest that wet-weather events commonly occurring during the wet-season may be contributing to the elevated wet-season observations. However, the elevated bacteria is not exclusive to the wet-season as illustrated by the variability in the dry-season samples. Although dry-season samples may be influenced by infrequent rainfall events, the variability may also be indicative of present wastewater sources contributing to bacteria levels year-round.

287

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-248. Seasonal variation at Pago Bay Duration Curve Analysis A duration curve framework is used in Figure 8-249, Figure 8-250, and Figure 8-251 to relate bacteria concentrations to hydrologic conditions. These figures reveal that concentrations two orders of magnitude beyond the WQS have occurred in both the wet and dry seasons and that most exceedances occur under high conditions. As shown in Figure 8-249, nearly 50 percent of samples taken during high flow conditions were greater than the instantaneous WQS. Wet-season and runoff observations characterized the majority of exceedances under high and moist flow conditions (Figure 8-250). Exceedances under low flow and dry flow conditions, however, were dominated by dry-season events. Notably, there are a number of runoff and wet-season events that did not result in exceedingly high bacteria concentrations indicating that runoff does not always result in elevated bacteria concentrations. Overall, a duration curve analysis of enterococci data at Pago Bay suggests that water quality exceedances are an issue at Pago Bay regardless of flow regime and season.

288

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-249. Water quality duration analysis of Pago Bay

Figure 8-250. Detailed water quality duration analysis of Pago Bay

289

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-251. Wet versus dry seasonal analysis for Pago Bay Potential Sources 5 The area draining to Pago Bay can be described as primarily vegetative cover with sparse development throughout. The developments are connected by a road network and they fall within single-family dwellings and agricultural use zoning (Figure 8-252). The Pago Bay site is immediately surrounded by single-family dwelling and multiple dwelling zonings (Figure 8-253). Although the land cover identifies limited areas of development, zoned designations indicate there is room for growth. There are no sewer lines that reach the Pago Bay shore, and the drainage area is heavily serviced by septic systems (Figure 8-252and Figure 8-253). Specific sources identified in Figure 8-252 that may be contributing to bacteria levels include a sewer connection and stormwater runoff. Pago Socio STP is located on the Pago Bay shore, which may be contributing elevated bacteria levels to Pago Bay and may be a considerable wastewater source. Guam EPA staff has identified septic systems, squatters, and river discharge as potential sources of bacteria to Pago Bay (Table 8-78). In addition, the limestone geology found along the eastern regions of Southern Guam can enhance the transport of bacteria (illustrated in Section 5 maps). The facile dissolution of limestone may create fractures in the bedrock inducing greater infiltrative capacities and increasing surface water-groundwater interactions.

290

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-252. Land cover and location of Pago Bay relative to potential source areas Table 8-78. Beach specific potential source summary (Site S-15: Pago Bay) Site ID

Wastewater S-15

Source Name (notes)

Type Septic systems Squatters Other

River discharge

291

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Figure 8-253. Location of Pago Bay relative to zoned land use Linkage Analysis The numeric target for this TMDL is Guamâ&#x20AC;&#x2122;s concentration-based criteria for enterococci bacteria in M-2 waters (i.e., a geometric mean of 35 counts / 100 mL and an instantaneous maximum of 104 counts / 100 mL). The relationship between this target and potential sources at Pago Bay is demonstrated through an analysis of water quality monitoring data at this site. A seasonal analysis, for example, demonstrates higher concentrations during the wet season, but significant variability is also apparent during the dry season. Further analysis demonstrates that elevated bacteria concentrations occur under all flow regimes during runoff, wet-season, and dry-season events. Water quality patterns do not suggest any strong driver influencing bacteria levels at Pago Bay, but potential sources in the drainage area do exist. Although disconnected, the impervious cover in the drainage area can serve as a mechanism of transporting upland bacteria sources to the Pago Bay via stormwater runoff. The quality of stormwater runoff from the drainage area can be impacted by the wastewater sources such as septic tanks found heavily dispersed throughout the area. Additionally, squatters and the Pago Socio STP, in the event of overflows or poor maintenance, may directly contribute to the quality of Pago Bay. Overall, a combination of stormwater and wastewater sources may be contributing to bacteria levels in Pago Bay. The technical analyses presented in this assessment of Pago Bay describe the relationship between water quality patterns and potential sources at this location. The TMDL set to the criteria values for enterococci bacteria will meet water quality standards and protect recreational uses at this beach.

292

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

TMDL Components Table 8-79 presents the TMDL for Pago Bay, identifying the loading capacity expressed as concentrationbased values for enterococci (allocations are identical to the loading capacity and are presented in Table 7-1). These concentration-based values apply across all flow zones. This TMDL uses an implicit MOS, described above in Section 7.3. Table 8-79 also shows the observed concentrations associated with each flow interval. The geometric mean of all samples at the TMDL site is presented as well as the 90th percentile of all samples, which is compared to the instantaneous WQS.

Table 8-79. TMDL summary (Site S-15: Pago Bay) Concentration by Duration Curve Zone (count/100 mL)

TMDL (count/ 100 mL)

High

Moist

Mid

Dry

Low

Geomean

121

Instantaneous

104

1,686

236

256

Measurement Type

Note:

Shaded cells indicate those zones where the criterion was exceeded. This is indicative of potential long term, chronic problems under those conditions.

A hydrology-based framework using duration curve zones allows the TMDL to evaluate monitoring data in a way that reflects major watershed processes indicative of different flows. This approach enables numeric targets in the TMDL to consider watershed processes, such as hydrology and source assessment information including land use. Table 8-80 identifies reductions for each duration curve zone by season by comparing observed summary statistics (geometric mean and 90th percentile) to the TMDL concentrations. These estimates can guide problem solving discussions on appropriate management strategies (based on knowledge associated with likely source areas, delivery mechanisms, and appropriate control measures that correspond to particular hydrologic conditions).

Table 8-80. Reductions required to meet the TMDL (Site S-15: Pago Bay) Reductions Required Dry Season Based on geometric mean Based on instantaneous maximum Wet Season Based on geometric mean Based on instantaneous maximum

Flow Condition (reductions expressed as percentage) High

Moist

Mid

Dry

Low

88% 97%

-----

--19%

70% 93%

--63%

--27%

-----

74% 96%

Note: --- indicates no reductions required for this condition

293

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

9. Implementation The focus of the implementation plan for the Bacteria TMDLs for Twenty-five Guam Beaches is to meet the recreational use goals and water quality standards for bacteria. The strength of a TMDL program lies in its ability to support development of information-based, water quality management strategies, a key for successful implementation planning. Basic components of the TMDL, namely the loading capacity and allocations, provide numeric targets that consider watershed processes, such as hydrology, as well as source assessment information including land use. These targets play a major role in building a problemsolving framework that guides development of an effective implementation program. Implementation planning typically identifies feasible and cost effective management measures capable of reducing pollutant loads to required levels. It is a key part of the water quality management process. TMDLs and implementation planning work together â&#x20AC;&#x201D;TMDLs provide the ability to support the development of information-based, water quality management strategies. This section serves as a guide to utilize the information presented in the TMDL and recommend implementation efforts that are effective and appropriate for each site. A major advantage of the duration curve framework used in this TMDL is the ability to provide meaningful connections between TMDL allocations and implementation efforts. The approach specifically allows implementers to link impairments to appropriate and potential sources based on the flow duration interval, or flow zone, in which that impairment occurs. Section 9.1 presents the reduction targets for each flow zone for each beach to assist in the prioritization of implementation activities. This section also offers a summary of beach impairments and associated issues related to each site to help prioritize sites. Section 9.2 characterizes and weighs sources identified at these sites to assist in the selection of the appropriate implementation activity, while Section 9.3 describes implementation activities and the sources they effectively address. Monitoring and other implementation recommendations are offered in Section 9.4.

9.1. Implementation Prioritization Prioritization of implementation activities begins with an assessment of the impairments at all twenty-five beaches. Percent reduction targets may be used to demonstrate the extent of impairments under each flow regime and can serve as measures of the actions necessary to restore water quality. In addition to percent reductions, driving factors influencing water quality can be used as measures of prioritizing beaches in need of implementation activities. Through the use of a flow duration curve approach, impaired water quality was associated with either wet-weather or dry-weather issues or sources. Reduction targets determined for the individual beaches are summarized in Table 9-1 through Table 9-4. Percent reduction targets are presented as geometric means and 90th percentiles for both wet and dry seasons. For each season, the geometric mean of the enterococci data for a given beach is compared to the geomean WQS and the same is done for the 90th percentile concentration to the instantaneous WQS. These percent reduction targets demonstrate the extent of impairment under each flow regime and are measures of the actions necessary to restore water quality. A high percent reduction indicates that water quality observed under that flow regime significantly exceeds water quality standards and action is required.

294

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 9-1. Summary of needed reductions to meet the TMDL (Geometric Mean – dry season) Water

Beach

Piti/Asan

Moist

Mid

Dry

Low

N-21

72%

---

N-22

53%

---

N-14

85%

47%

---

N-15

85%

10%

---

N-16

91%

47%

---

N-17

---

N-20

---

Outhouse Beach

N-18

---

Family Beach

N-19

---

S-02

69%

---

S-03

71%

---

S-17

84%

---

27%

S-04

95%

62%

28%

---

30%

S-05

76%

---

Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Port Authority Beach

Apra

Togcha Beach aka Agat Beach

Agat

Duration Curve Zone High

Beach at Fonte River, West HagåtñaBay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay

Fonte

Site ID

Taelayag

Beach South of Finile River Nimitz Beach

Umatac

Head of Umatac Bay

S-06

96%

51%

---

Toguan

Toguan Bay

S-07

99%

88%

32%

28%

10%

Geus

Merizo Public Pier Park

S-08

96%

57%

25%

Inarajan Pools

S-09

40%

---

Beach at Inarajan Bay

S-10

93%

70%

27%

---

Head of Talofofo Bay

S-11

99%

91%

66%

13%

S-18

---

S-12

---

S-13

---

YLIG

First Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park

S-14

---

Pago

Beach at Pago Bay

S-15

88%

---

Inarajan Talofofo

Togcha

Note:

A “---“ indicates that no reduction is necessary for that particular flow regime.

295

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 9-2. Summary of needed reductions to meet the TMDL (Geometric Mean – wet season) Water

Beach

Piti/Asan

Moist

Mid

Dry

Low

N-21

72%

---

N-22

---

N-14

83%

34%

16%

---

30%

N-15

52%

---

N-16

82%

51%

26%

---

N-17

---

N-20

---

23%

Outhouse Beach

N-18

---

Family Beach

N-19

---

S-02

78%

14%

---

75%

S-03

86%

---

55%

S-17

81%

---

46%

S-04

98%

79%

59%

37%

84%

S-05

84%

14%

---

70%

Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Port Authority Beach

Apra

Togcha Beach aka Agat Beach

Agat

Duration Curve Zone High

Beach at Fonte River, West HagåtñaBay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay

Fonte

Site ID

Taelayag

Beach South of Finile River Nimitz Beach

Umatac

Head of Umatac Bay

S-06

93%

30%

---

Toguan

Toguan Bay

S-07

95%

81%

64%

56%

---

Geus

Merizo Public Pier Park

S-08

89%

55%

33%

50%

---

Inarajan Pools

S-09

85%

11%

---

Beach at Inarajan Bay

S-10

97%

74%

30%

---

Head of Talofofo Bay

S-11

98%

92%

79%

48%

---

S-18

14%

---

S-12

---

S-13

84%

---

YLIG

First Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park

S-14

---

Pago

Beach at Pago Bay

S-15

70%

---

74%

Inarajan Talofofo

Togcha

Note:

A “---“ indicates that no reduction is necessary for that particular flow regime.

296

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 9-3. Summary of needed reductions to meet the TMDL (90th percentile – dry season) Water

Beach

Piti/Asan

Moist

Mid

Dry

Low

N-21

80%

63%

---

N-22

61%

---

N-14

82%

79%

57%

19%

35%

N-15

82%

70%

13%

---

N-16

95%

82%

47%

34%

42%

N-17

81%

---

N-20

23%

---

Outhouse Beach

N-18

83%

38%

---

Family Beach

N-19

---

S-02

98%

58%

15%

---

S-03

98%

32%

60%

---

S-17

99%

36%

51%

57%

35%

S-04

99%

89%

83%

47%

89%

S-05

94%

50%

30%

52%

13%

Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Port Authority Beach

Apra

Togcha Beach aka Agat Beach

Agat

Duration Curve Zone High

Beach at Fonte River, West HagåtñaBay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay

Fonte

Site ID

Taelayag

Beach South of Finile River Nimitz Beach

Umatac

Head of Umatac Bay

S-06

99%

92%

56%

---

Toguan

Toguan Bay

S-07

99%

71%

74%

51%

Geus

Merizo Public Pier Park

S-08

97%

94%

76%

58%

45%

Inarajan Pools

S-09

---

90%

---

Beach at Inarajan Bay

S-10

99%

87%

30%

51%

Head of Talofofo Bay

S-11

99%

98%

75%

42%

59%

S-18

---

15%

---

S-12

23%

---

S-13

---

YLIG

First Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park

S-14

---

Pago

Beach at Pago Bay

S-15

97%

---

19%

Inarajan Talofofo

Togcha

Note:

A “---“ indicates that no reduction is necessary for that particular flow regime.

297

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

Table 9-4. Summary of needed reductions to meet the TMDL (90th percentile – wet season) Water

Beach

Piti/Asan

Moist

Mid

Dry

Low

N-21

89%

48%

---

28%

N-22

62%

---

N-14

96%

69%

47%

---

69%

N-15

90%

---

44%

N-16

95%

84%

78%

39%

42%

N-17

---

N-20

---

67%

Outhouse Beach

N-18

---

Family Beach

N-19

---

S-02

97%

71%

20%

58%

95%

S-03

99%

72%

55%

24%

65%

S-17

99%

80%

51%

19%

55%

S-04

100%

96%

77%

81%

94%

S-05

99%

65%

27%

47%

78%

Beach at Piti Bay (Tepungan Beach) United Seamen's Service Beach (USO Beach) Port Authority Beach

Apra

Togcha Beach aka Agat Beach

Agat

Duration Curve Zone High

Beach at Fonte River, West HagåtñaBay West of Adelup Point, Asan Bay Asan Memorial Beach, Head of Asan Bay

Fonte

Site ID

Taelayag

Beach South of Finile River Nimitz Beach

Umatac

Head of Umatac Bay

S-06

99%

81%

56%

72%

---

Toguan

Toguan Bay

S-07

99%

97%

76%

85%

---

Geus

Merizo Public Pier Park

S-08

95%

82%

77%

82%

---

Inarajan Pools

S-09

99%

79%

---

Beach at Inarajan Bay

S-10

99%

94%

64%

58%

---

Head of Talofofo Bay

S-11

99%

97%

88%

66%

---

S-18

85%

---

S-12

27%

---

S-13

99%

76%

37%

---

YLIG

First Beach Ypan Beach Park Beach (Ipan Public Beach) Beach north of Togcha River Tagachan Beach Park

S-14

---

77%

Pago

Beach at Pago Bay

S-15

Inarajan Talofofo

Togcha

Note:

A “---“ indicates that no reduction is necessary for that particular flow regime.

Although percent reduction targets are useful in examining the extent of impairment and highlighting areas with the greatest need for water quality improvement, individual beach assessments enhance the implementation prioritization process. Water quality data analyses are essential in identifying exceedances; however, the application of water quality duration curves provides insight on the hydrologic conditions in which these exceedances occur. From these assessments, presented for each beach in Section 8, water quality patterns can help determine whether or not elevated bacteria is a wet-weather or dry-weather issue. Wet-weather bacteria sources are include stormwater runoff and other related issues such as SSOs. Wetweather issues are identified by exceedances occurring during the wet-season or during runoff events,

298

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

suggesting that stormwater runoff is a driving force in the presence and transport of bacteria. Wet-weather issues are not exclusive to stormwater sources as runoff can be influenced by the presence of wastewater sources. In fact, stormwater runoff can enhance the effects of local wastewater sources such as septic systems and leaky sewer mains that may be present. Beaches identified to have wet-weather issues have the most exceedances during the wet season, but can also have elevated bacteria during the dry season as a result of a rainfall event. Dry-weather issues are strongly driven by wastewater sources and, to a lesser extent, recreational and other sources. Dry-weather issues are identified by significantly high and consistent exceedances occurring during dry-weather or low flow conditions. Sources related to dry-weather issues generally provide a constant source of bacteria and can be point or non-point. Specific sources include wastewater sources such as failing septic systems, leaky sewer mains, inadequate STP discharges, and illicit or untreated sewage discharges. Other common dry-weather sources include marina and recreational activity, boat discharges, squatters, and wildlife. Dry-weather sources are most notable during dryweather conditions when stormwater does not play a role. Since these sources are constant in nature, elevated concentrations can be expected during dry periods in both the wet and dry seasons. Evaluation of water quality patterns and the use of water quality duration analyses define the extent of bacteria and shed light on whether these conditions are a result of wet-weather or dry-weather issues. The severity of the problem and whether the problem is a result of wet-weather or dry-weather sources can all play a role in prioritizing or classifying beaches in terms of implementation and water quality condition. Table 9-5 displays these parameters as well as the beach advisory frequency for each beach. This table can be used to prioritize or classify beaches based on the extent of impairment or related issues, thereby helping prioritize implementation efforts. Using the information presented in Table 9-5, implementation efforts can focus on specific sources where wet-weather or dry-weather issues have been identified. Sources are described in Section 9.2, while respective implementation measures are discussed below in Section 9.3.

Table 9-5. Priority beach implementation Site ID

Station Name*

% of High Flow Exceedances

% of Low Flow Exceedances

Beach Advisory Frequencies

N-21

Adelup Beach Park

48.72

4.44

36.98%

N-22

Adelup Point Beach (West of Adelup Park)

20.51

0.00

17.07%

N-14

Asan Bay Beach

66.67

15.56

52.32%

N-15

Piti Bay

42.31

8.89

90.05%

N-16

Santos Memorial Park Beach

64.10

17.78

N-17

United Seamen's Service

3.85

6.67

9.27%

N-20

Port Authority Beach

11.54

11.11

10.44%

N-18

Outhouse Beach

5.26

0.00

8.33%

Wet- or DryWeather + Issue

S S SR S SR S S S 299

Bacteria Total Maximum Daily Loads

Site ID

Station Name*

Twenty Five Guam Beaches

% of High Flow Exceedances

% of Low Flow Exceedances

Beach Advisory Frequencies 6.04%

N-19

Family Beach

3.90

0.00

S-02

Togcha Beach - Namo

52.94

26.32

S-03

Togcha Beach - Agat Bay

60.29

31.58

S-17

Togcha Beach - Beach at SCA

50.00

31.58

S-04

Bangi Beach

85.29

47.37

78.52%

S-05

Nimitz Beach

58.82

36.84

50.82%

S-06

Umatac Bay

78.95

7.69

45.05%

S-07

Toguan Bay

77.19

33.33

69.78%

S-08

Merizo Pier - Mamaon Channel

77.19

25.64

69.54%

S-09

Inarajan Pool

54.39

7.69

39.68%

S-10

Inarajan Bay

85.96

12.82

71.65%

S-11

Talofofo Bay

98.28

22.22

79.01%

S-18

First Beach - Talofofo

24.24

0.00

13.80%

S-12

Ipan Beach

17.54

0.00

4.12%

S-13

Togcha Bay - Talofofo

50.88

0.00

26.76%

S-14

Tagachang Beach

5.13

4.55

9.34%

S-15

Pago Bay

50.00

15.56

31.54%

75.24%

Wet- or DryWeather + Issue

S SR SR SR SR SR SR R R S SR SR S S S S SR

*High priority sites in bold-italic font. + S =wet-weather;R =dry-weather

9.2. Source Characterization Effective and successful implementation efforts start with the identification and characterization of sources contributing to water quality degradation. The duration curve framework applied in this TMDL uses flow duration intervals to serve as general indicators of hydrologic conditions (i.e., wet-weather event versus dry-weather event) to link impairments to source types and delivery mechanisms. Section 5identifies potential sources of bacteria pertinent to the impaired beaches and classifies the sources into three types: Stormwater, Wastewater, and Recreational and Other. A linkage between flow zone impairment and potential source type is demonstrated in Table 9-6, which can be used as a guide in assessing potential sources for the flow zone impairments summarized in Table 9-1 through Table 9-4 in Section 9.1 or in the individual beach assessments (Section 8). With this guide, impairments in specific

300

Bacteria Total Maximum Daily Loads

Twenty Five Guam Beaches

flow zones can be attributed to specific source types and thereby addressed with appropriate implementation efforts.

Table 9-6. Source categories identified using a duration curve framework. Flow Zone High

Moist

Mid-Range

Dry

Low

Stormwater

Source Category Wastewater

Recreational and Other

Individual beach assessments (Section 8) identify specific sources ofbacteria that fall within each beach’s drainage area. These potential sources have been identified based on information provided by Guam EPA staff and GIS data. Source types and affiliated specific sources include:

− −

Stormwater (surface runoff, highway runoff)

− −

Recreation (marina, boating, tourism activities)

Wastewater (septic systems, SSO, POTW, sewer lines, industrial point sources [GPA effluent]) Other Sources (wildlife, transient populations [squatters], historical Confined Animal Feeding Operations [CAFO], upland sources via river discharge)

Stormwater sources represent runoff from all types of surfaces including impervious cover and roadway cover. These sources are often tied to highly developed and/or populated areas and affect water quality generally during the wet-season where rainfall events most occur. Impairments under mid-range, moist, and high flow conditions are most representative of the effects of stormwater runoff. Wastewater sources are typically non-transient and serve as a continuous source of bacteria. The effect of these sources are most notable during the dry conditions; however, they can be an issue under all flow regimes. Recreational and other sources are driven by water activities and transient activities such as wildlife and squatters. Like wastewater sources, recreational and other sources can be present during any weather condition; however, their effects are most noticeable under low-flow conditions. To help prioritize implementation efforts, a summary of potential sources for each beach is presented in Table 9-7. Sources are classified as major (l) or minor (¡)to demonstrate the extent of their influence on water quality. This classification was determined based on the water quality patterns demonstrated in the RBMP monitoring data and the application of the flow duration curve approach. A source is designated as major if it coincides with the wet-weather or dry-weather issues identified for that site. A source is designated as minor if that source does not overlap with the site-specific issues. For sites where both wetand dry-weather issues have been identified, all potential sources have been deemed as major contributors. Implementation opportunities associated with these sources are described in the next section.

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Table 9-7. Beach-specific bacteria sources

l

N-14

Asan Bay Beach*

N-15

Piti Bay*

N-16 N-17

Santos Memorial Park Beach United Seamen's Service

N-18

Outhouse Beach

N-19

Family Beach

N-20

Port Authority Beach

S-02 S-03 S-17

Togcha Beach Namo Togcha Beach - Agat Bay* Togcha Beach Beach at SCA

¡

l

¡

l

¡

l

l l

l

l l l

l

l ¡

l

¡

l

¡

l

l l l l l

River Discharge

¡

Historical Confined Animal Feedlot (Chicken)

¡

Wildlife

Adelup Point Beach (West of Adelup Park)*

Squatters

N-22

Recreational & Tourism Activities

l

Boat Discharge

¡

Recreational and Other Sources

Highway Maintenance and Runoff Marina and Recreational Boating

¡

Stormwater Sources

Stormwater Runoff

SSO

Adelup Beach Park*

Station Name

Industrial point source (GPA effluent)

Sewer Lines

N-21

Site ID

POTW

Septic Systems

Wastewater Sources

l l l l

l

S-04

Bangi Beach

l

S-05

Nimitz Beach*

l

S-06

Umatac Bay

l

S-07

Toguan Bay*

S-08

Merizo Pier Mamaon Channel

S-09

Inarajan Pool

¡

S-10

Inarajan Bay

l

S-11

Talofofo Bay

l

S-18

First Beach - Talofofo

¡

S-12

Ipan Beach

¡

S-13

Togcha Bay Talofofo

S-14

Tagachang Beach

¡

S-15

Pago Bay

l

Note:

* Identifies beaches where GIS data have identified untreated sewage discharges in the area. These sources have been classified as SSOs.

l l l

l l ¡ l l l

l

¡

l

l ¡ l l

l l

l

l l

l

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9.3. Implementation Activities Successful implementation will likely require the use of many management options due to the high required reductions for bacteria loads to many of the impaired beaches. Implementation activities to address bacteria should include existing programs and plans, as well as specific implementation opportunities to address loads from all sources. Table 9-8 summarizes whether a source can be addressed by Guam’s existing programs and/or if it can be addressed by additional specific best management practices(BMPs). This section describes the programmatic implementation options currently in place and suggests specific BMP activities for each source. A combination of these practices can lead to bacteria reductions. The results from Table 9-5 and Table 9-7 can be linked to the solution options presented in Table 9-8, providing the framework for a comprehensive management plan for each beach toreduce bacteria loads.

Table 9-8. Source-specificimplementation opportunities

River Discharge

Historical Confined Animal Feedlot (Chicken)

Wildlife

Squatters

Recreational & Tourism Activities

Boat Discharge

Recreational and Other Sources

Marina and Recreational Boating

Highway Maintenance and Runoff

Stormwater Runoff

Stormwater Sources

Industrial point source (GPA effluent)

POTW

SSO

Solution Opportunity

Sewer Lines

Septic Systems

Wastewater Sources

Programmatic Implementation Opportunities NPDES Permits and Section 401 Water Quality Certification Individual Wastewater System Permits

•

• •

Storm Water Management

•

• •

•

Coastal Nonpoint Control Program (CNCP) Recreational Water Use Management Plan Guam’s Marina Rules and Regulations Clean Marina Advisory Group

•

• •

•

Additional Management Implementation Opportunities Non-structural (NS) Solutions Residential Stormwater Education Campaign Septic Systems

•

Recreational and Transient population Outreach Wildlife Management Proper Pet Waste Education and Outreach Program Structural (S) Solutions Private Retrofits Open Space Opportunities Urban Retrofits Animal Waste Management

• • • • • •

• • • •

• •

• • • 303

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9.3.1. Existing Programs A number of programs exist that address documented water quality problems on Guam’s beaches. Several programs are implemented by Guam EPA, which are specifically designed to address known sources of pollution including pipes, ditches, and sanitary or storm sewers. Others rely on efforts of partner agencies. If fully implemented, measurable reductions in bacteria levels could lead to achievement of the TMDLs. Key programs include: • NPDES Permits and Section 401 Water Quality Certification • Individual Wastewater System Permits • Stormwater Management A brief description of each program is provided in the following sections. Key aspects of these efforts that will lead to reductions in bacteria concentrations are discussed below. The connection between the duration curve framework and development of management strategies is illustrated in Table 9-9. Potential implementation opportunities are identified including the flow zones where theycan be most effective. For example, GWA’s efforts to address sewage infrastructure problems (notably pump station failures and sewer overflows) are targeted to prevent delivery of bacteria that could occur under any flow conditions. The TMDL analysis in Table 9-7 demonstrates specific beaches where these problems are a likely source of bacteria.

Table 9-9. Implementation programs highlighted using a duration curve framework. Flow Zone High

Moist

Mid-Range

Dry

Low

Storm Water Management

Implementation Programs

GWA Sewerage System Improvements to Address Pump System Failures and Reduce Sewer System Overflows Individual On-site Waste Water Permits, Sanitary Survey & Enforcement, and Sewer Connections Implement Waste Water Treatment Plant Improvements through NPDES Permits Marina Management

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NPDES Permits and Section 401 Water Quality Certification National Pollutant Discharge Elimination System (NPDES) permits in Guam are issued by USEPA Region 9. These permits can include stormwater and non-stormwater sources (note: stormwater sources are discussed separately below). Non-stormwater permitted facilities that potentially affect beaches in the TMDL project area are listed inTable 5-2. Guam EPA’s Water Pollution Control (WPC) Program in coordination with the Environmental Planning and Review Division are responsible for certifying all permit applications. During certification, conditions and abatement schedules for each permit are recommended. The guidelines for effluent limitations in each permit are based on the revised 2001 Guam Water Quality Standards. The WPC Program oversees implementation and compliance of conditions imposed by Guam EPA §401 Water Quality Certification for NPDES permits issued to industrial and non-industrial facilities. All permittees are monitored by both WPC Program and USEPA staff to ensure compliance with applicable permit requirements and schedules. The Water Pollution Control Act and Guam Water Quality Standards authorize Guam EPA to take legal action against those who pollute island waters. Enforcement is carried out through scheduled site and sampling inspections. NPDES permittees submit quarterly Discharge Monitoring Reports (DMRs) to USEPA Region 9 for review and evaluation. Appropriate enforcement action is applied for non-compliance to approved permit conditions. One major action resulting from NPDES compliance efforts is the GWA Stipulated Order for Preliminary Relief. This Order is one key part towards solving water quality problems in the TMDL project area. The Order outlines a list of mandated actions for GWA, including the development and implementation of a comprehensive Water Master Plan. The Order also addresses the financing of wastewater capital improvement projects. Continued compliance with the GWA Stipulated Order will improve water quality as a result of infrastructure improvements to sewage treatment plants, pump stations, and ground water facilities. Completion of the Water Master Plan provides a strategic roadmap for the utility to meet the wastewater treatment needs in the TMDL project area. This includes bacteria contamination of the TMDL beaches that are associated with compliance issues at the two wastewater treatment facilities. The Order will also address water quality problems adversely affecting beaches on the §303(d) list that are associated with pump station failures and SSOs.

Individual Wastewater System Permits A number of problems discussed in the individual beach assessments are the result of inadequate on-site wastewater treatment. The concerns arise both in non-sewered areas, as well as in areas where residences have not yet connected to available sewer systems. Guam EPA’s Integrated Report indicates that domestic wastewater associated with population increase is the largest potential source of pollution to all waters of Guam. Due to economic difficulties, development associated with the population increase can occur without adequate sewage infrastructure. As a result, occupants depend on septic tank and leaching field systems for waste disposal.

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Guam’s Eastern shore has a highly permeable geologic layer. Population development in this area can lead to a high density of septic systems with insufficient and poorly maintained sewage treatment systems leaking through the permeable geologic layer to underlying aquifers. The combination of these factors can also affect beaches in the TMDL project area. A key implementation tool to control this source of pollution is set forth in Section 48102, Chapter 48 of 10 Guam Code Annotated (GCA). This rule requires that no building shall be occupied or used as a dwelling, school, public building, commercial building, industrial building or place of assembly without toilet or sewage facilities of a type inspected and approved for the disposition of human excreta and other domestic wastes. Permits are required for new and remodeled buildings. In order to ensure the installation of proper sewage disposal systems, the permitting process includes mandatory on-site inspection and building plan review, permit issuance and final inspection of the completed disposal system. Building occupancy permits are only issued upon approval of the structure’s sewage disposal system. Another part of this program is sanitary surveys conducted by Guam EPA staff. For example, approximately 125 buildings were connected to the public sewer system in 2006 as a result of sanitary surveys and enforcement action. In 2007 Guam EPA staff concentrated on identifying strategic Northern locations with available sewer systems. Subsequently, sanitary surveys were conducted of those residences with or without connections to the nearby systems. Enforcement action is forthcoming. A focus on continued sanitary surveys in areas that contribute to bacterial pollution of beaches in the TMDL project area is another key part of addressing documented water quality problems.

Stormwater Management Stormwater management is another key part of efforts to reduce bacterial contamination in the TMDL project area. Although the projected 2007 population of the island was over 170,000, Guam has not been previously covered under the USEPA MS4 program. The 2010 census designated the area of Hagåtña as urban clusters rather than urbanized area, and in February 2011 a request for designation of MS4 discharges on the Island of Guam for NPDES permit coverage was filed.Specifically, all Guam MS4s are designated for NPDES permitting. An MS4 permit covering the entire island is forthcoming and is expected to be issued by late 2012 or mid-2013. This TMDL will be incorporated into the permit for the relevant drainage areas. In the interim, stormwater management in the TMDL project area must rely on coordination between an array of Guam agencies and other local efforts. Guam EPA has made great improvements towards implementing stormwater management through requirements under its Nonpoint Source Management Program. Large and commercial developments are required to submit “Best Management Practices” for the total elimination of stormwater discharges to nearshore waters of Guam. Guam EPA and the Commonwealth of the Northern Mariana Islands (CNMI) have collaborated to produce a technical guidance document that governs stormwater planning and design in both Guam and the CNMI. This effort took advantage of the geographic proximity of the islands and their similar climatic regimes, as well as local studies. The purpose of the CNMI / Guam Storm Water Management Manual and accompanying regulations is:

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• to protect the waters of the CNMI and Guam from the adverse impacts of urban stormwater runoff; • to provide design guidance on the most effective BMPs for new development sites and redevelopment sites both during post construction; and • to improve the quality of BMPs that are constructed in the CNMI and Guam, specifically in regard to their performance, longevity, safety, ease of maintenance, community acceptance and environmental benefit. Guam EPA requires that all stormwater disposal for new facilities be contained on-site, up to the 20-year, 24-hour storm event. Permits for and upgrades to stormwater management systems are required to accommodate large expected increases to flows and decreases to quality of the stormwater, whether discharged to the ground or to surface waters. Prior to finalizing the Guam / CNMI Stormwater Manual, Executive Order 2005-35 was promulgated on October 21, 2005. This provided interim adoption of stormwater management criteria for the Department of Public Works (DPW) and other government of Guam projects. Guam EPA is in the process of developing local stormwater regulations based on criteria in the Guam / CNMI Stormwater Manual. Guam EPA intends to incorporate them into a revision / update of current soil erosion and sediment control regulations. Upon approval and adoption, such regulations will be applicable to and enforceable upon both public and private sector communities.

Other Programs The Coastal Zone Act Reauthorization Amendments (CZARA) was passed by Congress to address nonpoint source pollution in coastal waters. Section 6217 of CZARA requires states and territories (including Guam) to develop Coastal Nonpoint Pollution Control Programs. The Coastal Nonpoint Program builds upon existing state coastal zone management and water quality programs by applying a consistent set of economically achievable management measures to prevent and mitigate polluted runoff. These measures are designed to control runoff from six main sources: • • • • • •

Urban areas Marinas Forestry Agriculture Hydromodification (shoreline and stream channel modification) Loss of wetlands and riparian areas

State coastal nonpoint programs implement the measures and provide accountability through a variety of tools, including rules, ordinances, voluntary approaches, educational campaigns and financial incentives, all backed by enforceable policies and mechanisms. In its program, a state or territory describes how it will implement nonpoint source pollution control management measures. If the original management measures fail to produce the necessary coastal water quality improvements, a state or territory then must implement additional management measures to address remaining water quality problems. Guam’s Coastal Nonpoint Control Program (CNPCP) was approved in 2007. The approval document describes mechanisms in place that Guam can use to control runoff from nonpoint sources. Urban programs were described earlier in this section under stormwater management. Designation of the urban 307

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portions of Guam to be subject to NPDES MS4 permit requirements is an option that would strengthen the stormwater management program relative to TMDL implementation. In fact, the water quality benefits to be achieved under an NPDES MS4 permit were noted in the final decision document approving Guam’s CNPCP. The final decision document approving Guam’s CNPCP also describes mechanisms in place to address water quality problems associated with marinas. The primary mechanisms in place to address pollution problems associated with marinas rely on Guam’s Water Quality Standards and Marina Rules and Regulations of the Port Authority of Guam (Marina Rules and Regulations). Guam’s Marina Rules and Regulations address vessel, property or facility cleanliness and sanitation (Section 4.02); management, control and disposal of shipboard solid waste (Section 4.03); and disposal of any litter, sewage, or other gaseous, liquid or solid materials into the water (Section 4.06 and 4.07). Guam’s Recreational Water Use Management Plan (RWUMP) establishes rules to regulate uses of recreational and commercial watercraft within the waters of Guam. In addition to these regulatory components, Guam has laid out a process and timeline for developing a comprehensive clean marina program. The Clean Marina Advisory Group has identified and is beginning to implement priority actions to reduce nonpoint source pollution from Guam’s marinas, including installing hazardous waste storage containers and wash down facilities at the two most heavily used marinas. The Advisory Group is also improving public outreach and education by installing educational signage about clean marina BMPs at the marinas and working closely with the Port Authority of Guam as it updates its marina rules and regulations to incorporate additional clean marina BMPs. If these programs fail to address problems associated with marinas, another option is be to explore the use of a Multi-Sector General Permit under the NPDES program. Marinas are a designated SIC category under EPA’s stormwater management rules. A permit could be issued with appropriate conditions that would lead to achieving water quality standards and TMDL targets.

Military Expansion The Guam Civilian / Military Task Force (GCMTF) was created by Executive Order 2006-10 to create an integrated comprehensive master plan that will address issues related to the military buildup. The purpose of this master plan is to maximize opportunities resulting from this expansion for the benefit of the civilian and military community. An Environment Sub-Committee to this Task Force has been created under the lead of Guam EPA. This Sub-Committee must determine environmental concerns including adverse effects projected to occur off Department of Defense (DOD) properties. Activities associated with the military buildup will have a direct effect on efforts to implement these Guam bacteria TMDLs. One of the more significant impacts is the increased pressure on the wastewater infrastructure system. GWA is already conducting activities under a Stipulated Order to address documented problems that lead to beach advisories. This includes sewage overflows, pump station failures, and wastewater treatment plant performance. Potential effects of the military expansion on efforts by local agencies to implement the TMDL need to be recognized and addressed in the planning and funding process.

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Similarly, the increased population associated with the military expansion includes not only direct personnel, but also dependents, construction and support staff. The increased numbers of people will undoubtedly use the existing road system and commercial facilities in the TMDL project area. Individual beach assessments identified several locations where improved stormwater management is a key to successful implementation. As local agencies work to improve stormwater management, DOD can clearly help provide leadership in implementing solutions. An example is DOD’s efforts to implement the Energy Independence and Security Act. Section 438 of this legislation establishes strict stormwater runoff requirements for Federal development and redevelopment. The Navy, for instance, has a policy that requires the implementation of Low Impact Development (LID). The Navy’s experience and expertise in the application of LID could serve as a technical resource for local agencies in their efforts to improve stormwater management in the TMDL project area.

9.3.2. Specific Implementation Opportunities (BMPs) The following section provides a summary of specific implementation opportunities that could be used in support of TMDL implementation and, ultimately, the attainment of standards. Both structural and nonstructural BMPs offer the potential to reduce pollution from several sources of bacteria to Guam’s beaches. Non-structural BMPs aim to prevent runoff stormwater from a site and are, therefore, often referred to as pollution prevention or source control BMPs. Once site runoff has occurred, structural BMPs can be implemented to infiltrate, filter, and treat stormwater runoff. Examples of structural and non-structural BMPs for each applicable source are discussed in the following sections. 9.3.2.1. Non-structural BMPs Non-structural BMPs reduce the exposure of materials to stormwater, and thereby reduce the amount of pollutants picked up by stormwater. It is typically more cost-effective to prevent pollution from entering stormwater rather than to treat the collected stormwater flow or water bodies affected by stormwater discharges (UDFCD 2010). Traditional source control methods include land use or site planning practices, as well as structures and ordinances that aim to prevent urban runoff, therefore, reducing runoff from the source of pollution. Examples of source control BMPs are listed below and each is discussed in more detail in the remainder of this section:

ü ü ü ü ü

Residential Stormwater Education Campaign Septic System Education Campaign Recreational and Transient Population Outreach Wildlife Management Proper Pet Waste Education and Outreach Campaign

During the early stages of implementation, efforts should first focus on the refinement of existing programs to verify that they target bacteria sources effectively. The following provides a summary of non-structural implementation categories that could be used in support of TMDL implementation and the attainment of standards.

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Residential Stormwater Education Campaign Targeted education and outreach should explore ways to encourage downspout disconnection in residential areas. The primary objective of a disconnection program is the reduction of stormwater runoff volumes and peak flows. Residential Implementation Recommendations: Downspout Disconnection: In many cases, residential gutter systems are piped, and discharge to receiving streets or alley-ways. This can increase runoff (especially peak-flow) amounts. Efforts should be made to encourage disconnection and redirection of downspouts to landscape features built to increase infiltration.

Septic Systems Septic systems are a predominate source of bacteria to the Guam Beaches and they may be a small, but important, contributor to upstream loadings. When not maintained properly, septic systems can cause the release of pathogens, as well as excess nutrients into surface waters.The most effective BMP for managing loads from septic systems is regular maintenance. Unfortunately, most people do not think about their wastewater systems until a malfunction or failure occurs. Education is a crucial component for reducing potential upstream bacteria loadings and could be used in addition to existing permitting and survey efforts detailed in the Individual Wastewater System Permits section. Septic System Recommendation: Septic Education: Many homeowners are not familiar with EPA recommendations concerning maintenance schedules. Annual inspections in addition to regular maintenance ensure that systems are functioning properly. An inspection program would help identify those systems that are not functioning properly. Encourage homeowners to inspect systems annually and pump systems every 3 to 5 years, depending on the tank size and number of residents per household. To avoid collapsed pipes, educate homeowners to avoid driving heavy equipment above a septic system. To prevent septic systems from overflowing, encourage water conservation, avoid diverting guttersand/or basement pumps into septic systems and avoid disposing of trash through drains or toilets.

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Recreational and Transient Population Solutions There are vast opportunities for public access to Guamâ&#x20AC;&#x2122;s beaches. Opportunities include swimming, snorkeling, and scuba diving amongst others. In addition to recreational users, a sizeable transient population frequents the Pago Bay area and other waterways of near TMDL beaches. Several implementation opportunities are available to address these sources. Recreational and Transient Population Recommendations: Targeted Outreach Activities: Targeted outreach could focus on additional signage to encourage proper waste disposal. Since a large population of transient persons frequents the area near Pago Bay, it is suggested that elements of an outreach program be targeted at this audience and location. Improve Facilities Located Near Beaches: Itis important to evaluate the need for additional facilities (i.e., trash receptacles and restrooms) surrounding high-use areas along Guamâ&#x20AC;&#x2122;s beaches. Additional facilities that are then utilized by the population can have a relatively quick impact on reducing highly localized sources of bacteria.

Wildlife Management Wildlife and, in particular, feral pigs, have been identified as a likely source of bacteria to Guamâ&#x20AC;&#x2122;s beaches. A concerted effort should be made by Guam staff (including maintenance and transportation staff) to ensure that wildlife (feral pigs) are properly managed, and/or future introductions of wildlife in to the area are minimized or prevented. Wildlife Management Implementation Recommendations: Monitoring: To measure the effectiveness of wildlife management efforts, and establish baseline conditions, focused monitoring should be conducted prior to any management activity. Animal excrement must also be removed from (and/or prevented from reaching) the stormwater system. Because the objective of this monitoring effort would be to evaluate short-term trends, it is suggested that staff monitor for five days prior and five days immediately following the completion of management. Recommendations for weekly monitoring following management to determine the lasting effectiveness of wildlife management is also suggested. Development of Wildlife Management Plan: Guam staff should explore the need to develop a wildlife management plan to address animals (specifically feral pigs) in the stormwater system. Wildlife Relocation: Animal relocation (or removal) could be conducted.

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Proper Pet Waste Education and Outreach Campaign Pollution prevention programs that focus on pet waste management can help limit the bacteria reaching waterways via stormwater runoff. Pet waste management controls bacteria loading to the waters of Guam at the source. Pet Waste Management Recommendations: Increase Pet Waste Outreach and Education in the Water Education Program: Guam EPA should look for ways to expand pet waste management education and outreach programs. Activities could include public service announcements, bus advertisements, pledge programs, and interactive websites with surveys. Develop a recognizable ‘Scoop the Poop’ campaign: A campaign refers to a coordinated, comprehensive outreach effort that integrates a variety of education and outreach techniques. Campaign development starts with a baseline survey to understand existing dog owner behaviors and perceptions (i.e., why owners fail to pick up waste), uses survey information to craft effective messages delivered using formats tailored to target audiences, and follows up with a postcampaign survey to determine effectiveness. 9.3.2.2. Structural BMPs Structural BMPs can be incorporated in urban landscapes to capture, infiltrate, filter, and treat stormwater runoff. When selecting the most appropriate BMPs for a specific site or drainage area, site-specific conditions (e.g., land availability, slope, soil characteristics, climate condition, utilities, and characterization of contributing drainage including imperviousness, etc.) must be taken into consideration. Care must also be given to ensure that proper treatment identifies any site concerns or hazards. For example, infiltration should not be encouraged in areas surrounding stormwater ‘hot spots’ such as automotive repair shops, gasoline stations, or industrial areas where groundwater contamination or pollutant transfer is a possibility. Infiltration techniques may also not be appropriate in areas at risk of media clogging. This could include areas near restaurants where the possibility of oil and grease contamination exists. Alternatively, in areas where groundwater contamination is not a concern, structural BMPs can incorporate infiltration as well as other treatment techniques to effectively reduce treatment volume and flow rates. The use of BMPs is quickly advancing and new research is supporting the use of varying BMPs for bacteria removal, provided the systems are constructed and maintained properly (Hathaway et al. 2011; Hathaway and Hunt 2012; Hunt et al. 2008). Theses BMPs can provide other water quality benefits by reducing runoff amounts; therefore, reducing the amount of bacteria and other pollutants washed from surfaces. The first step toward use of structural BMPs would include conducting a needs and feasibility assessment, followed by a conceptual designs phase. During this first step, Guam EPA staff must work with other departments to determine whether BMPs are allowed or how they can be incorporated in the rights-ofway. Since a number of municipal barriers (e.g., codes and ordinances) may prevent the incorporation of BMPs, staff should begin addressing these limitations before too much time passes. It is likely that fewer

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barriers will prevent the use of BMPs on open spaces and residential properties and so, these opportunities should be explored soon after a TMDL implementation program is in place. Structural BMP opportunities discussed in the following sections include: ü ü ü ü

Private retrofits Open space opportunities Urban retrofits Animal Waste Management

Private retrofits Compared to right-of-way enhancements that will likely require concerted planning and financial resources, private retrofits on residential or commercial properties may exist. A private retrofit program should encourage homeowners or commercial property owners to disconnect gutter downspouts from streets and alley-ways, and redirect these flows to landscape features or rain storage devices designed to infiltrate or store stormwater. Potential private retrofit BMPs include rain gardens (bioretention), filter strips and buffers, and rain barrels. Residential Implementation Recommendations: Needs Feasibility Study: Evaluate existing partnerships and programs to determine potential resources to initiate a private retrofit program. Evaluate neighborhoods to determine physical feasibility and areas that would provide the greatest benefit from the program. Focus should be placed on storm drain basins identified as a concern in the TMDL. Continued Monitoring: Staff should work with private property owners to characterize baseline conditions and measure effectiveness of a retrofit program. Monitoring should include evaluation of volume and pollutant reductions.

Open space opportunities Open spaces, parks, and schools provide unique opportunities to incorporate larger-scale BMPs that can be designed to treat a sizeable upstream drainage area. Appropriate larger-scale BMPs include: detention and retention ponds, grass swales and constructed wetlands. In addition to water quality enhancements, when constructed and maintained properly, these BMPs can enhance the natural setting and provide educational opportunities. Research recently conducted by EPA, Office of Research and Development, used pilot-scale projects to evaluate processes occurring within constructed wetlands and retention ponds. Results from this effort indicate that water temperature, light and a combination of other factors influenced bacteria concentrations. The research also suggests that both constructed wetlands and retention ponds reduced concentrations of bacteria in urban stormwater and that bacteria tended to accumulate in sediments, which could maintain background levels of bacteria (Struck et al. 2008). This finding suggests that BMPs which 313

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reduced turbidity also showed significant reduction in bacteria concentrations. Another study found that wetlands and bioretention areas can result in bacteria removal of 50 percent or greater (Hathaway et al. 2009). Because these systems have been shown to provide a reduction in bacteria (with proper design and maintenance), these types of practices are recommended for feasibility analyses of implementation in appropriate areas. It is also recommended that these systems be used in combination as a â&#x20AC;&#x2DC;treatment trainâ&#x20AC;&#x2122; so that the cumulative results yield maximum reductions. Open Space Implementation Recommendations: Needs and Feasibility Study: Identify locations and assess the needs and opportunities specific to each location. Conceptual Design: Develop conceptual designs specific to key areas, including the quantification of flow/loading reductions. Pilot Study: Select a key pilot study project from information gathered in the feasibility study and conceptual design phase. Conduct water quality monitoring (wet weather) to establish baseline conditions. Install pilot project, with care to include signage to increase public awareness and understanding. Once established, monitor to measure effectiveness and gauge the potential use of similar methods throughout the drainage.

Urban retrofits With proper design and maintenance, urban retrofit BMP projects can successfully reduce flows and pollutant loading in urban environments. BMP methods most appropriate for urban areas generally include linear bioretention units, planter boxes, and proprietary BMPs. Similar to larger scale BMPs, smaller linear bioretention cells have also been shown to reduce loadings of bacteria and other pollutants. In addition to these water quality improvements, curbbump-outs, can improve the urban environment and calm traffic, creating a more pedestrian friendly environment. Urban Retrofit Implementation Recommendations: Needs and Feasibility Study: Identify locations and assessment the needs and opportunities specific to each location. Conceptual Design: Develop conceptual designs specific to key areas, including the quantification of flow/loading reductions. Pilot Study: Select a key pilot study project from information gathered in the feasibility study and conceptual design phase. Conduct water quality monitoring (wet weather) to establish baseline conditions. Install pilot project, with care to include signage to increase public awareness and understanding. Once established, monitor to measure effectiveness and gauge the potential use of similar methods throughout the drainage area.

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Animal Waste Management Historically, runoff from a confined chicken feedlot drained to Santos Memorial Park Beach. Ensuring proper waste management is essential to keeping bacteria from feedlots from entering the waters draining to Santos Memorial Park Beach. Animal Waste Management Implementation Recommendations: Waste Management Facility: Evaluate potential waste management for the CFO including a dike, water and sediment control basin, waste storage facility, or a wastewater lagoon.

9.4. Monitoring and TMDL Re-Assessment Monitoring is an important element of implementation planning because it produces data needed to refine management strategies. Monitoring data often enables the overall water quality management process to incorporate adaptive management concepts. The application of the duration curve framework allows water quality monitoring information to be used in a way that characterizes concerns and describes patterns associated with impairments. Continued data collection at these twenty-five beaches under the RBMP will provide information that enables these TMDLs to be evaluated in terms of progress towards achieving Guamâ&#x20AC;&#x2122;s Water Quality Standards (especially temporal evaluations). In addition to monitoring bacteria, continuous monitoring of turbidity is also suggestedin that further investigation may reveal a relationship with bacteria. If a relationship can be established, turbidity monitoring may provide a less expensive and quicker means of sampling as a surrogate to absent bacteria measurements. NPDES permits are re-issued every 5 years and the Â§303(d) impaired waters list is re-assessed every 2 years. Because a number of critical implementation actions are connected to compliance with the permits, a TMDL re-evaluation schedule will be developed by Guam EPA in collaboration with USEPA. If sufficient progress has not been made during the re-evaluation timeframe, the TMDLs may be re-opened. Sufficient progress is defined as removal of at least 50% (or twelve of the twenty-five beaches) from the impaired waters list. Any adjustments to wasteload and load allocations needed to meet water quality standards will be incorporated into revised TMDLs.

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10. References Guam EPA (Guam Environmental Protection Agency). 2001. Guam Water Quality Standards. Water Programs Division. Barrigada, Guam. Guam EPA (Guam Environmental Protection Agency). 2003. Recreational Beach Monitoring Plan: Guam Coastal Waters. Recreational Beach Monitoring Program. Environmental Monitoring and Assessment Division. Barrigada, Guam. Guam EPA (Guam Environmental Protection Agency).2006. 2006 Integrated Report. Water Programs Division. Barrigada, Guam. Guam EPA (Guam Environmental Protection Agency). 2010. 2010 Integrated Report. Water Programs Division. Barrigada, Guam. Hathaway, J.M., W.F. Hunt, S.J. Jadlocki. 2009. Indicator Bacteria Removal in Stormwater Best Management Practices in Charlotte, North Carolina. Journal of Environmental Engineering, 135(12), 1257-2185. Hathaway, J.M., W.F. Hunt, A.K. Graves, J.D. Wright. 2011. Field Evaluation of Bioretention Indicator Bacteria Sequestration in Wilmington, NC. Journal of Environmental Engineering. 137(12): 11031113. Hathaway, J.M. and W.F. Hunt. 2012. Indicator Bacteria Performance of Stormwater Control Measures in Wilmington, NC. Journal of Irrigation and Drainage Engineering. 138(2): 185-197. Hunt, W.F., J.T. Smith, S.J. Jadlocki, J.M. Hathaway, and P.R. Eubanks. 2008. Pollutant Removal and Peak Flow Mitigation by a Bioretention Cell in Urban Charlotte, NC. Journal of Environmental Engineering. 134(5): 403-408. Leopold, L.B. 1994. A View of the River. Harvard University Press. Cambridge, MA. Struck, S., A. Selvakumar, M. Borst. 2008. Predication of Effluent Quality from Retention Ponds and Constructed Wetlands for Managing Bacterial Stressors in Storm-Water Runoff. J. of Irrigation and Drainage Engin. September/October 2008. Tetra Tech, Inc. 2012. Flow Estimation in Southern Guam using an LSPC Watershed Model. Technical memorandum developed for Guam EPA and USEPA. September 2012. Urban Drainage and Flood Control District (UDFCD). 2010. Urban Storm Drainage Criteria Manual Volume 3- Best Management Practices. November 2010. Denver, Colorado. USEPA (U.S. Environmental Protection Agency). 1999. Draft Guidance for Water Quality-based Decisions: The TMDL Process (Second Edition). Office of Water. EPA-841-D-99-001. Washington, DC. USEPA (U.S. Environmental Protection Agency). January 2001. Protocol for Developing Pathogen TMDLs. Office of Water. EPA-841-R-00-002. Washington, DC.

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USEPA (U.S. Environmental Protection Agency). August 2007. An Approach for Using Load Duration Curves in the Development of TMDLs. EPA 841-B-07-006. Office of Wetlands, Oceans, and Watersheds. Washington, DC.http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/techsupp.cfm USEPA (U.S. Environmental Protection Agency). 2012. BEACON 2.0 - Beach Advisory and Closing Online Notification. Online query of BEACON 2.0 performed in September 2012 for Guam Beach Advisories 2001-2011. http://watersgeo.epa.gov/BEACON2//reports.html USEPA (U.S. Environmental Protection Agency) Region 9 and Guam EPA (Guam Environmental Protection Agency). 2009. Development of Guam Northern Watershed Bacteria TMDLs. December 2009. Prepared by Tetra Tech, Inc.

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